bzoj1600

n 条边围成 n 边形的条件。。。。

#include<bits/stdc++.h>using namespace std;#define FOR(i,s,t) for(int i=(s);i<=(t);i++)inline int read(void){    int x = 0, c, f = 1;    do{c=getchar();if(c=='-')f=-1;}while(c<'0'||c>'9');    do{x=x*10+c-'0';c=getchar();}while(c>='0'&&c<='9');    return x * f;}typedef long long LL;LL f[2555][5];int main(){    f[0][0] = 1;    int n = read(), mx = (n + 1) / 2 - 1;    for (int i = 1; i <= 4; i++)        for (int j = 1; j <= n; j++)            for (int k = 1; k <= min(j,mx); k++)                f[j][i] += f[j - k][i - 1];    cout << f[n][4] << endl;}