HDU2200

水题～～～
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 1 /*
 2 C(N,M)
 3 */
 4 #include<stdio.h>
 5 #include<string.h>
 6 #include<stdlib.h>
 7 #include<algorithm>
 8 #include<iostream>
 9 #include<queue>
10 #include<stack>
11 #include<math.h>
12 #include<map>
13 typedef __int64 int64;
14 using namespace std;
15 const int maxn = 1005;
16 int64 solve( int64 n,int64 m ){
17     int64 sum=1;
18     int64 tt=1;
19     for( int64 i=n;i>=n-m+1;i-- ){
20         sum=sum*i/tt;
21         tt++;
22     }
23     return sum;
24 }    
25 int main(){
26     int64 n;
27     while( scanf("%I64d",&n)!=EOF ){
28         int64 sum=0;
29         for( int64 i=2;i<=n;i++ ){
30             sum+=( solve( n,i )*( i-1 ) );
31         }
32         printf("%I64d\n",sum);
33     }
34     return 0;
35 }
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