USACO3.43Electric Fence(pick定理）

忘记pick定理是什么了 想枚举来着 。。没枚出来

有篇pick定理的证明 貌似挺好 也没太看懂

 /*
     ID: shangca2
     LANG: C++
     TASK: fence9
  */
 #include <iostream>
 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #include<stdlib.h>
 using namespace std;
 int gcd(int x,int y)
 {
     return y==?x:gcd(y,x%y);
 }
 int main()
 {
     freopen("fence9.in","r",stdin);
     freopen("fence9.out","w",stdout);
     int n,m,p,k=,ans;
     double s;
     cin>>n>>m>>p;
     s = p*m/2.0;
     k+=p;
     k+=gcd(n,m);
     k+=abs(gcd(n-p,m));
     ans = (s+)-k/;
     cout<<ans<<endl;
     return ;
 }