#include <iostream>
#include <cstdio>
#include <vector>

using namespace std;
vector <long long> p;
int main()
{
    freopen("pascal.in","r",stdin);
    freopen("pascal.out","w",stdout);
    int n,d;
    scanf("%d %d", &n, &d);
    for(int i=0;i<n;i++)
    {
        p.push_back(1);
        if(p.size()>2)
        {
            for(int i=p.size()-2;i>=1;i--)
                p[i]+=p[i-1];
        }
    }
    cout<<p[d];
    return 0;
}