diff --git a/Day12.cs b/Day12.cs
index 6360dfd..ce7a158 100644
--- a/Day12.cs
+++ b/Day12.cs
@@ -1,6 +1,7 @@
 #define Day12
 #if Day12
 using System.Collections.Immutable;
+using System.Diagnostics;
 using AoC2021;
 const string START = "start";
 const string END = "end";
@@ -65,4 +66,29 @@ long PathCountPart2(Dictionary<string, ImmutableHashSet<string>> paths, Immutabl
 
     return count;
 }
+
+// Part Two iteratively
+long count = 0;
+var states = new Stack<State>();
+states.Push(new State(ImmutableHashSet.Create(START), START, false));
+while (states.Count > 0) {
+    var s = states.Pop();
+    count += paths[s.current].Contains(END) ? 1 : 0;
+    ImmutableHashSet<string> adjacent;
+    if (s.twice) {
+        adjacent = paths[s.current].Except(s.visitedSmallCaves).Remove(END);
+    } else {
+        adjacent = paths[s.current].Remove(END);
+    }
+    foreach (var a in adjacent) {
+        if (Char.IsLower(a[0])) {
+            states.Push(new State(s.visitedSmallCaves.Add(a), a, s.twice || s.visitedSmallCaves.Contains(a)));
+        } else {
+            states.Push(new State(s.visitedSmallCaves, a, s.twice));
+        }
+    }
+}
+Console.WriteLine(count);
+
+record State(ImmutableHashSet<string> visitedSmallCaves, string current, bool twice);
 #endif
\ No newline at end of file