diff --git a/2016/d23/ex1/ex1.py b/2016/d23/ex1/ex1.py
new file mode 100755
index 0000000..80f79fb
--- /dev/null
+++ b/2016/d23/ex1/ex1.py
@@ -0,0 +1,87 @@
+#!/usr/bin/env python
+
+import collections
+import enum
+import sys
+from typing import NamedTuple
+
+
+class Op(enum.StrEnum):
+    CPY = "cpy"
+    INC = "inc"
+    DEC = "dec"
+    JNZ = "jnz"
+    TGL = "tgl"
+
+
+class Instruction(NamedTuple):
+    op: Op
+    x: str
+    y: str | None = None
+
+    @classmethod
+    def from_str(cls, input: str) -> "Instruction":
+        op, *rest = input.split()
+        return cls(Op(op), *rest)
+
+    def toggle(self) -> "Instruction":
+        if self.y is None:
+            op = Op.DEC if self.op == Op.INC else Op.INC
+        else:
+            op = Op.CPY if self.op == Op.JNZ else Op.JNZ
+        return Instruction(op, self.x, self.y)
+
+
+def solve(input: str) -> int:
+    def parse(input: str) -> list[Instruction]:
+        return [Instruction.from_str(line) for line in input.splitlines()]
+
+    def resolve(y: str | None, registers: dict[str, int]) -> int:
+        assert y is not None  # Sanity check
+        try:
+            return int(y)
+        except ValueError:
+            return registers[y]
+
+    instructions = parse(input)
+    registers: dict[str, int] = collections.defaultdict(int)
+
+    ip = 0
+    registers["a"] = 7
+    while True:
+        if ip < 0 or ip >= len(instructions):
+            break
+        instr = instructions[ip]
+        ip += 1
+        match instr.op:
+            case Op.CPY:
+                assert instr.y is not None
+                if instr.y.isdigit():
+                    continue
+                registers[instr.y] = resolve(instr.x, registers)
+            case Op.INC:
+                if instr.x.isdigit():
+                    continue
+                registers[instr.x] += 1
+            case Op.DEC:
+                if instr.x.isdigit():
+                    continue
+                registers[instr.x] -= 1
+            case Op.JNZ:
+                if resolve(instr.x, registers) != 0:
+                    ip += resolve(instr.y, registers) - 1  # Account auto-increment
+            case Op.TGL:
+                target = ip + resolve(instr.x, registers) - 1  # Account auto-increment
+                if target < 0 or target >= len(instructions):
+                    continue
+                instructions[target] = instructions[target].toggle()
+    return registers["a"]
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()