diff --git a/sample/day3-sample.txt b/sample/day3-sample.txt
new file mode 100644
index 0000000..f274bda
--- /dev/null
+++ b/sample/day3-sample.txt
@@ -0,0 +1 @@
+xmul(2,4)%&mul[3,7]!@^do_not_mul(5,5)+mul(32,64]then(mul(11,8)mul(8,5))
diff --git a/sample/day3-sample2.txt b/sample/day3-sample2.txt
new file mode 100644
index 0000000..159557d
--- /dev/null
+++ b/sample/day3-sample2.txt
@@ -0,0 +1,2 @@
+xmul(2,4)&mul[3,7]!^don't()_mul(5,5)+mul(32,64](mul(11,8)undo()?mul(8,5))
+
diff --git a/src/day3_p1.gleam b/src/day3_p1.gleam
new file mode 100644
index 0000000..983555d
--- /dev/null
+++ b/src/day3_p1.gleam
@@ -0,0 +1,97 @@
+import gleam/int
+import gleam/io
+import gleam/iterator
+import gleam/list.{reverse, take_while}
+import gleam/option.{type Option, None, Some}
+import gleam/string.{join}
+import stdin.{stdin}
+
+pub fn main() {
+  stdin()
+  |> read_input
+  |> find_and_calculate(0)
+  |> io.debug
+}
+
+type FindResult {
+  Expression(Int, Int, String)
+  Nothing
+}
+
+fn find_and_calculate(s: String, acc: Int) -> Int {
+  // Drop all until first 'mul('
+  let next =
+    string.crop(from: s, before: "mul(")
+    |> string.drop_start(up_to: 4)
+
+  case next {
+    "" -> acc
+    str -> {
+      case find_expression(str) {
+        Expression(a, b, rest) -> find_and_calculate(rest, acc + a * b)
+        Nothing -> find_and_calculate(next, acc)
+      }
+    }
+  }
+}
+
+fn find_expression(str: String) -> FindResult {
+  case
+    str
+    |> read_num
+    |> then(read_char(","))
+    |> then(read_num)
+    |> then(read_char(")"))
+  {
+    Some(#(#(#(#(a, _), b), _), rest)) -> Expression(a, b, rest)
+    None -> Nothing
+  }
+}
+
+fn read_char(char: String) {
+  fn(str: String) -> Option(#(String, String)) {
+    case string.pop_grapheme(str) {
+      Ok(#(ch, rest)) if ch == char -> Some(#(char, rest))
+      _ -> None
+    }
+  }
+}
+
+fn then(
+  current: Option(#(a, String)),
+  next: fn(String) -> Option(#(b, String)),
+) -> Option(#(#(a, b), String)) {
+  case current {
+    None -> None
+    Some(#(a, s)) ->
+      next(s)
+      |> option.map(fn(result) {
+        let #(b, rest) = result
+        #(#(a, b), rest)
+      })
+  }
+}
+
+const numbers = "0123456789"
+
+fn read_num(str: String) -> Option(#(Int, String)) {
+  let to_parse =
+    str
+    |> string.to_graphemes
+    |> take_while(fn(c) { string.contains(does: numbers, contain: c) })
+    |> join(with: "")
+
+  to_parse
+  |> int.parse
+  |> option.from_result
+  |> option.map(fn(n) {
+    #(n, string.drop_start(str, up_to: string.length(to_parse)))
+  })
+}
+
+fn read_input(it: iterator.Iterator(String)) -> String {
+  it
+  |> iterator.fold([], fn(acc, line) { [line, ..acc] })
+  |> reverse
+  |> join(with: "")
+}
diff --git a/src/day3_p2.gleam b/src/day3_p2.gleam
new file mode 100644
index 0000000..2aff4cb
--- /dev/null
+++ b/src/day3_p2.gleam
@@ -0,0 +1,96 @@
+import gleam/int
+import gleam/io
+import gleam/iterator
+import gleam/list.{reverse, take_while}
+import gleam/option.{type Option, None, Some}
+import gleam/string.{join}
+import stdin.{stdin}
+
+pub fn main() {
+  stdin()
+  |> read_input
+  |> find_and_calculate(0, can_mul: True)
+  |> io.debug
+}
+
+type FindResult {
+  Expression(Int, Int, String)
+  Nothing
+}
+
+fn find_and_calculate(s: String, acc: Int, can_mul mul_enabled: Bool) -> Int {
+  case s {
+    "" -> acc
+    "do()" <> rest -> find_and_calculate(rest, acc, can_mul: True)
+    "don't()" <> rest -> find_and_calculate(rest, acc, can_mul: False)
+    "mul(" <> rest if mul_enabled -> {
+      case find_expression(rest) {
+        Expression(a, b, rest) ->
+          find_and_calculate(rest, acc + a * b, can_mul: mul_enabled)
+        Nothing -> find_and_calculate(rest, acc, can_mul: mul_enabled)
+      }
+    }
+    _ -> find_and_calculate(string.drop_start(s, 1), acc, can_mul: mul_enabled)
+  }
+}
+
+fn find_expression(str: String) -> FindResult {
+  case
+    str
+    |> read_num
+    |> then(read_char(","))
+    |> then(read_num)
+    |> then(read_char(")"))
+  {
+    Some(#(#(#(#(a, _), b), _), rest)) -> Expression(a, b, rest)
+    None -> Nothing
+  }
+}
+
+fn read_char(char: String) {
+  fn(str: String) -> Option(#(String, String)) {
+    case string.pop_grapheme(str) {
+      Ok(#(ch, rest)) if ch == char -> Some(#(char, rest))
+      _ -> None
+    }
+  }
+}
+
+fn then(
+  current: Option(#(a, String)),
+  next: fn(String) -> Option(#(b, String)),
+) -> Option(#(#(a, b), String)) {
+  case current {
+    None -> None
+    Some(#(a, s)) ->
+      next(s)
+      |> option.map(fn(result) {
+        let #(b, rest) = result
+        #(#(a, b), rest)
+      })
+  }
+}
+
+const numbers = "0123456789"
+
+fn read_num(str: String) -> Option(#(Int, String)) {
+  let to_parse =
+    str
+    |> string.to_graphemes
+    |> take_while(fn(c) { string.contains(does: numbers, contain: c) })
+    |> join(with: "")
+
+  to_parse
+  |> int.parse
+  |> option.from_result
+  |> option.map(fn(n) {
+    #(n, string.drop_start(str, up_to: string.length(to_parse)))
+  })
+}
+
+fn read_input(it: iterator.Iterator(String)) -> String {
+  it
+  |> iterator.fold([], fn(acc, line) { [line, ..acc] })
+  |> reverse
+  |> join(with: "")
+}