51nod 1120 机器人走方格 V3

#include <bits/stdc++.h>using namespace std;long long mod=10007;long long powmod(long long x,long long p){long long ret=1;while(p){if(p&1)ret=ret*x%mod;x=x*x%mod;p>>=1;}return ret;}long long C(long long n,long long m){long long i,j,ret=1,div=1;for(i=n,j=1;j<=m;i--,j++){ret=ret*i%mod;div=div*j%mod;}ret=ret*powmod(div,mod-2)%mod;return ret;}long long lucas(long long n,long long m){if(m)return C(n%mod,m%mod)*lucas(n/mod,m/mod);elsereturn 1;}int main(){long long n;while(cin>>n){cout<<2*lucas(2*(n-1),n-1)*powmod(n,mod-2)%mod<<endl;}}