hdu 2200 Eddy's AC难题

 1 #include <iostream>
 2 #include <cstring>
 3 #include <cstdio>
 4 #include <string>
 5 #include <iomanip>
 6 #include <algorithm>
 7 #include <queue>
 8 #include <vector>
 9 #include <map>
10 using namespace std;
11 long long  cal(long long  n, long long  x){
12     long long  sum = 1;
13     for(int i = 1; i <= x; i++){
14         sum = sum*(n-i+1)/i;
15     }
16     return sum;
17 }
18 int main(){
19     long long N, sum;
20     while(cin>>N){
21         sum = 0;
22         for(long long i = 2; i <= N; i++){
23             sum += (i-1)*cal(N, i);
24         }
25         cout<<sum<<endl;
26     }
27     return 0;
28 }