문제출처 : https://www.acmicpc.net/problem/11050
code
#include <iostream>
using namespace std;
int main()
{
ios::sync_with_stdio(false);
int N, K, a=1, b=1, i;
cin >> N >> K;
for (int i = 0; i < K; i++)
{
a = a * (N - i);
b = b * (i + 1);
}
cout << a / b;
return 0;
}