diff --git a/AdventOfCode2025/day5/bin/dune b/AdventOfCode2025/day5/bin/dune
new file mode 100644
index 0000000..406ffc0
--- /dev/null
+++ b/AdventOfCode2025/day5/bin/dune
@@ -0,0 +1,4 @@
+(executable
+ (public_name day5)
+ (name main)
+ (libraries day5))
diff --git a/AdventOfCode2025/day5/bin/main.ml b/AdventOfCode2025/day5/bin/main.ml
new file mode 100644
index 0000000..9cc0bec
--- /dev/null
+++ b/AdventOfCode2025/day5/bin/main.ml
@@ -0,0 +1,144 @@
+let get_range str =
+    let list = (String.split_on_char '-' str) 
+        |> List.map int_of_string in
+
+    assert (List.length list == 2);
+    
+    let lower = List.nth list 0 in
+    let upper = List.nth list 1 in
+
+    (lower, upper)
+
+let is_item_in_range  i (lower, upper) = 
+    lower <= i && i <= upper
+
+let rec list_some l fn = 
+    match l with 
+    | [] -> false
+    | head :: tail -> if fn head then true else list_some tail fn
+
+let is_item_in_ranges ranges i =
+    list_some ranges (is_item_in_range i)
+
+
+let is_overlapping (lower1, upper1) (lower2, upper2) =
+    lower1 <= lower2 && lower2 <= upper1 ||
+    lower2 <= lower1 && lower1 <= upper2
+
+let get_combined_ranges (lower1, upper1) (lower2, upper2) =
+    let lower = min lower1 lower2 in
+    let upper = max upper1 upper2 in
+    (lower, upper)
+
+let non_overlapping_ranges_work ranges =
+    let rec loop acc changes ranges =
+        match ranges with 
+        | [] -> (acc, changes)
+        | head :: tail -> 
+            let overlap_fn = is_overlapping head in
+            let overlapping_index = List.find_index overlap_fn tail in
+            match overlapping_index with
+            | Some r -> 
+                let (l, u) = List.nth tail r in
+                let tail_without_index = List.filter 
+                    (fun (lower, upper) -> not (lower == l && upper == u)) tail in
+                let combined_range = get_combined_ranges head (l, u) in
+                loop (combined_range :: acc) true (tail_without_index)
+            | None -> loop (head :: acc) changes tail
+    in
+    loop [] false ranges
+
+(* let rec print_ranges l = *)
+(*     match l with  *)
+(*     | [] -> print_endline ""; *)
+(*     | (lower, upper) :: tail ->  *)
+(*         Printf.printf "lower=%d,upper=%d\n" lower upper; *)
+(*         print_ranges tail *)
+        
+
+let rec non_overlapping_ranges ranges =
+    let (ranges, changes)  = non_overlapping_ranges_work ranges in
+    if changes then non_overlapping_ranges ranges
+    else ranges
+
+    
+let solve lines = 
+    let no_empty_lines = List.filter (fun i -> String.length i > 0) lines in
+    let (ranges, items) = List.partition (fun i -> String.contains i '-') no_empty_lines in
+
+    let ranges = List.map get_range ranges in
+    let items = List.map int_of_string items in
+
+    let part1 = List.fold_left (
+        fun acc i -> if is_item_in_ranges ranges i then acc + 1 else acc
+    ) 0 items in
+
+    let ranges = non_overlapping_ranges ranges in
+     
+    let part2 = List.fold_left (
+        fun acc (lower, upper) -> acc + (upper - lower + 1)
+    ) 0 ranges in
+
+    (part1, part2)
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+let read_lines name =
+  let ic = open_in name in
+  let try_read () = try Some (input_line ic) with End_of_file -> None in
+  let rec loop acc =
+    match try_read () with
+    | Some s -> loop (s :: acc)
+    | None ->
+        close_in ic;
+        List.rev acc
+  in
+  loop []
+
+let () =
+print_endline "Day 5";
+  let part1, part2 =
+    read_lines "./input.txt" |> solve
+  in
+  Printf.printf "Part 1: %s\nPart 2: %s\n" (string_of_int part1)
+    (string_of_int part2)
+
+
diff --git a/AdventOfCode2025/day5/day5.opam b/AdventOfCode2025/day5/day5.opam
new file mode 100644
index 0000000..a43bbcb
--- /dev/null
+++ b/AdventOfCode2025/day5/day5.opam
@@ -0,0 +1,32 @@
+# This file is generated by dune, edit dune-project instead
+opam-version: "2.0"
+synopsis: "A short synopsis"
+description: "A longer description"
+maintainer: ["Maintainer Name <maintainer@example.com>"]
+authors: ["Author Name <author@example.com>"]
+license: "LICENSE"
+tags: ["add topics" "to describe" "your" "project"]
+homepage: "https://github.com/username/reponame"
+doc: "https://url/to/documentation"
+bug-reports: "https://github.com/username/reponame/issues"
+depends: [
+  "dune" {>= "3.20"}
+  "ocaml"
+  "odoc" {with-doc}
+]
+build: [
+  ["dune" "subst"] {dev}
+  [
+    "dune"
+    "build"
+    "-p"
+    name
+    "-j"
+    jobs
+    "@install"
+    "@runtest" {with-test}
+    "@doc" {with-doc}
+  ]
+]
+dev-repo: "git+https://github.com/username/reponame.git"
+x-maintenance-intent: ["(latest)"]
diff --git a/AdventOfCode2025/day5/dune-project b/AdventOfCode2025/day5/dune-project
new file mode 100644
index 0000000..5a70a7f
--- /dev/null
+++ b/AdventOfCode2025/day5/dune-project
@@ -0,0 +1,26 @@
+(lang dune 3.20)
+
+(name day5)
+
+(generate_opam_files true)
+
+(source
+ (github username/reponame))
+
+(authors "Author Name <author@example.com>")
+
+(maintainers "Maintainer Name <maintainer@example.com>")
+
+(license LICENSE)
+
+(documentation https://url/to/documentation)
+
+(package
+ (name day5)
+ (synopsis "A short synopsis")
+ (description "A longer description")
+ (depends ocaml)
+ (tags
+  ("add topics" "to describe" your project)))
+
+; See the complete stanza docs at https://dune.readthedocs.io/en/stable/reference/dune-project/index.html
diff --git a/AdventOfCode2025/day5/lib/dune b/AdventOfCode2025/day5/lib/dune
new file mode 100644
index 0000000..2de91f0
--- /dev/null
+++ b/AdventOfCode2025/day5/lib/dune
@@ -0,0 +1,2 @@
+(library
+ (name day5))
diff --git a/AdventOfCode2025/day5/test/dune b/AdventOfCode2025/day5/test/dune
new file mode 100644
index 0000000..15d4eea
--- /dev/null
+++ b/AdventOfCode2025/day5/test/dune
@@ -0,0 +1,2 @@
+(test
+ (name test_day5))
diff --git a/AdventOfCode2025/day5/test/test_day5.ml b/AdventOfCode2025/day5/test/test_day5.ml
new file mode 100644
index 0000000..e69de29