diff --git a/BestCoder/Round-80/1002.cpp b/BestCoder/Round-80/1002.cpp
new file mode 100644
index 0000000..7779d0e
--- /dev/null
+++ b/BestCoder/Round-80/1002.cpp
@@ -0,0 +1,44 @@
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+using namespace std;
+long long q_mul( long long a, long long b, long long mod ) //快速计算 (a*b) % mod
+{
+    long long ans = 0;  // 初始化
+    while(b)                //根据b的每一位看加不加当前a
+    {
+        if(b & 1)           //如果当前位为1
+        {
+            b--;
+            ans =(ans+ a)%mod;   //ans+=a
+        }
+        b /= 2;                         //b向前移位
+        a = (a + a) % mod;          //更新a
+
+    }
+    return ans;
+}
+
+int main()
+{
+    int t;
+    scanf("%d",&t);
+    while(t--)
+    {
+        long long q,p;
+        scanf("%I64d %I64d",&q,&p);
+        long long a=q-1;
+        long long b=q-2;
+        long long ans;
+        if(a%2==0)
+        {
+            ans=q_mul(a/2,b,p);
+        }
+        else
+        {
+            ans=q_mul(a,b/2,p);
+        }
+        printf("%I64d\n",ans);
+    }
+    return 0;
+}