#include <iostream>

using namespace std;


int main() {
    int n;
    cout<<" enter value of n :"<<endl;
    cin>>n;
    int r;
    cout<<" enter value of r : "<<endl;
    cin>>r;
    int a;
    a=1;
    for(int i =1; i<=n; i++){
        a=i*a;
    }
    int b;
    b=1;
    for(int i=1; i<=r; i++){
        b=i*b;
    }
    int c;
    c=1;
    for(int i=1; i<=n-r; i++){
        c=i*c;
}
    cout<<a/(b*c);
}