//-----------------------------------
//EX0403.cpp
//组合数
//-----------------------------------
#include<iostream>
using namespace std;
//-----------------------------------
int compo(int n, int m){
if(n-m < m) m =n-m;
int t=1;
for(int i=1; i<=m; ++i)
t = t*(n-i+1)/i;
return t;
}//----------------------------------
int main(){
cout<<compo(18, 13)<<"\n";
}//----------------------------------