#include<stdio.h>

int combination (int n,int r){
    int bunshi=1;
    int bunbo=1;
    for(int i=r;i>=1;i--){
        bunshi=bunshi*i;
    }
    for(int i=0;i<r;i++){
        bunbo=bunbo*(n-i);
    }
    return bunbo/bunshi;
}
int main(){
    printf("%d\n",combination(5,2));
    printf("%d\n",combination(6,3));
    printf("%d\n",combination(7,4));
}