diff --git a/2020.csproj b/2020.csproj
index f2f965e..0763a40 100644
--- a/2020.csproj
+++ b/2020.csproj
@@ -71,6 +71,9 @@
     <None Update="22input.txt">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </None>
+    <None Update="23input.txt">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
   </ItemGroup>
 
 </Project>
diff --git a/23input.txt b/23input.txt
new file mode 100644
index 0000000..88666bb
--- /dev/null
+++ b/23input.txt
@@ -0,0 +1 @@
+538914762
\ No newline at end of file
diff --git a/Program.cs b/Program.cs
index 8bc120b..5bdc916 100644
--- a/Program.cs
+++ b/Program.cs
@@ -25,6 +25,7 @@
          Q20.Go();
          Q21.Go();
          Q22.Go();
+         Q23.Go();
          Util.Log($"Total time={(System.DateTime.Now - start).TotalMilliseconds}ms");
       }
    }
diff --git a/Q23.cs b/Q23.cs
new file mode 100644
index 0000000..b2078dc
--- /dev/null
+++ b/Q23.cs
@@ -0,0 +1,144 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+
+namespace _2020
+{
+   class Q23
+   {
+      static readonly List<int> list = new List<int>();
+
+      public static void Go()
+      {
+         var start = DateTime.Now;
+         MakeList();
+         Util.Log($"Q23 MakeList took {(DateTime.Now - start).TotalMilliseconds}ms");
+         var p1start = DateTime.Now;
+         Part1();
+         Util.Log($"Q23 part1 took {(DateTime.Now - p1start).TotalMilliseconds}ms");
+         var p2start = DateTime.Now;
+         Part2();
+         Util.Log($"Q23 part2 took {(DateTime.Now - p2start).TotalMilliseconds}ms");
+
+         Util.Log($"Q23 took {(DateTime.Now - start).TotalMilliseconds}ms");
+      }
+
+      static void MakeList()
+      {
+         var text = File.ReadAllText("23input.txt");
+         foreach (var ch in text)
+         {
+            list.Add(Convert.ToInt32(ch.ToString()));
+         }
+      }
+
+      static int mod(int x, int m)
+      {
+         int r = x;
+         if (r >= x)
+         {
+            r = x % m;
+         }
+         return r < 0 ? r + m : r;
+      }
+
+      static void Part1()
+      {
+         var cupList = new List<int>(list);
+         var currentCupVal = cupList[0];
+         var currentCupIdx = 0;
+         var pickedUp = new int[3];
+         for (int move = 0; move < 100; move++)
+         {
+            for (int i = currentCupIdx + 1, pickedUpIdx = 0; pickedUpIdx < 3; pickedUpIdx++)
+            {
+               if (i >= cupList.Count)
+               {
+                  i = 0;
+               }
+
+               pickedUp[pickedUpIdx] = cupList[i];
+               cupList.RemoveAt(i);
+            }
+
+            var destCupVal = currentCupVal - 1;
+            var destCupIdx = cupList.IndexOf(destCupVal);
+            while (destCupIdx < 0)
+            {
+               destCupVal = mod(destCupVal - 1, cupList.Count + pickedUp.Length + 1);
+               destCupIdx = cupList.IndexOf(destCupVal);
+            }
+
+            cupList.InsertRange(destCupIdx + 1, pickedUp);
+            currentCupVal = cupList[mod(cupList.IndexOf(currentCupVal) + 1, cupList.Count)];
+            currentCupIdx = cupList.IndexOf(currentCupVal);
+         }
+
+         var startIdx = cupList.IndexOf(1);
+         var scoreStr = "";
+         for (var idx = startIdx + 1; scoreStr.Length < cupList.Count - 1; idx++)
+         {
+            scoreStr += cupList[idx % cupList.Count].ToString();
+         }
+
+         Util.Log($"Q23Part1: labels={scoreStr}");
+      }
+
+      static void Part2()
+      {
+         var cupList = new List<int>(list);
+         var highestVal = cupList.Aggregate(0, (result, curr) => curr > result ? curr : result);
+         for (int i = cupList.Count, next = highestVal + 1; i < 1000000; i++, next++)
+         {
+            cupList.Add(next);
+         }
+
+         var currentCupVal = cupList[0];
+         var currentCupIdx = 0;
+         var pickedUp = new int[3];
+         var start = DateTime.Now;
+         var lastMove = 0;
+         for (int move = 0; move < 10000000; move++)
+         {
+            for (int i = currentCupIdx + 1, pickedUpIdx = 0; pickedUpIdx < 3; pickedUpIdx++)
+            {
+               if (i >= cupList.Count)
+               {
+                  i = 0;
+               }
+
+               pickedUp[pickedUpIdx] = cupList[i];
+               cupList.RemoveAt(i);
+            }
+
+            var destCupVal = currentCupVal - 1;
+            var destCupIdx = cupList.IndexOf(destCupVal);
+            while (destCupIdx < 0)
+            {
+               destCupVal = mod(destCupVal - 1, cupList.Count + pickedUp.Length + 1);
+               destCupIdx = cupList.IndexOf(destCupVal);
+            }
+
+            cupList.InsertRange(destCupIdx + 1, pickedUp);
+            currentCupVal = cupList[mod(cupList.IndexOf(currentCupVal) + 1, cupList.Count)];
+            currentCupIdx = cupList.IndexOf(currentCupVal);
+
+            var dt = DateTime.Now - start;
+            var dtSeconds = dt.TotalSeconds;
+            if (dtSeconds >= 1.0)
+            {
+               start = DateTime.Now;
+               var rate = (move - lastMove) / dtSeconds;
+               lastMove = move;
+               var remainingMoves = 10000000 - move;
+               var endTime = DateTime.Now + TimeSpan.FromSeconds(remainingMoves / rate);
+               Util.Log($"Current rate: {rate:N1} mps, {remainingMoves:N} moves remaining. Should be done by {endTime}");
+            }
+         }
+
+         var oneIdx = cupList.IndexOf(1);
+         Util.Log($"Q23Part2: next two={cupList[(oneIdx + 1) % cupList.Count]}, {cupList[(oneIdx + 2) % cupList.Count]}, multiplied={1L * cupList[(oneIdx + 1) % cupList.Count] * cupList[(oneIdx + 2) % cupList.Count]}");
+      }
+   }
+}