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 }