#include <iostream>
using namespace std;

int countSelections(int n, int m) {
    if (m == 0) return 1;
    if (n <= 0 || m < 0) return 0;
    if (m == 1) return n; // 选1本有n种选法
    
    return countSelections(n - 1, m) + countSelections(n - 2, m - 1);
}

int main() {
    int n, m;
    cin >> n >> m;
    cout << countSelections(n, m) << endl;
    return 0;
}