#include <iostream>
using namespace std;
int n, a, b;
unsigned long long fac(int n) {
    long long f = 1;
    for (int i = n; i > 0; i--) f *= i;
    return f;
}
unsigned long long C (int s, int m) {
    return fac(s) / (fac(s - m) * fac(m));
}
int main () {
    unsigned long long ans = 0;
    cin >> n >> a >> b;
    for(int i = 0; i <= a; i++)
        for(int j = 0; j <= b; j++)
            ans += C(n + i - 1, n - 1) * C(n + j - 1, n - 1);
    cout << ans;
    return 0;
}