diff --git a/animation-simulation/求次数问题/只出现一次的数.md b/animation-simulation/求次数问题/只出现一次的数.md
index d8a792e..140029f 100644
--- a/animation-simulation/求次数问题/只出现一次的数.md
+++ b/animation-simulation/求次数问题/只出现一次的数.md
@@ -51,6 +51,7 @@ class Solution {
                 return y;
             }
         }
+        return -1;
     }
 }
 ```