diff --git a/source/Trek-12/ConsoleApp/Program.cs b/source/Trek-12/ConsoleApp/Program.cs
index adc70f7..828b022 100644
--- a/source/Trek-12/ConsoleApp/Program.cs
+++ b/source/Trek-12/ConsoleApp/Program.cs
@@ -240,11 +240,17 @@ class Program
             op = Console.ReadLine();
         }
         int test = Convert.ToInt32(op);
+        
         while(((Game)sender).UsedMap.CheckOperationPossible(test-1))
         {
             Console.WriteLine("Invalid operation. Please choose again.");
             Console.WriteLine();
             op = Console.ReadLine();
+            while (op != "1" && op != "2" && op != "3" && op != "4" && op != "5")
+            {
+                Console.WriteLine("Invalid operation. Please choose again.");
+                op = Console.ReadLine();
+            }
             test = Convert.ToInt32(op);
         }