diff --git a/TangDou/Topic/SpareTire.cpp b/TangDou/Topic/SpareTire.cpp
index ad949b8..9b26fd3 100644
--- a/TangDou/Topic/SpareTire.cpp
+++ b/TangDou/Topic/SpareTire.cpp
@@ -59,6 +59,7 @@ signed main() {
                     s *= p[j];
                 }
 
+            // https://www.cnblogs.com/xiuwenli/p/9610029.html
             // 比如找到了s=6=2*3，需要知道s是奇数个，还是偶数个因子
             // n/s:范围内6的倍数有多少个
             int k = n / s;