#include <bits/stdc++.h>

using namespace std;
long long countArray(int n, int r) {
    if(r > n / 2) r = n - r; // because C(n, r) == C(n, n - r)
    long long ans = 1;
    int i;

    for(i = 1; i <= r; i++) {
        ans *= n - r + i;
        ans /= i;
    }

    return ans;
}

int main() {
    int n;
    int k;
    int x;
    cin >> n >> k >> x;
    long long answer = countArray(k, n-2);
    cout << answer << endl;
    return 0;
}