#include <bits/stdc++.h>
using namespace std;
long double t, n, m;
long double C(long double n, long double k) {
  long double ret = 1;
  for (long double i = n; i > n - k; i--) ret *= i;
  for (long double i = k; i >= 1; i--) ret /= i;
  return ret;
}
int main() {
  cin >> n >> m >> t;
  long double b, g, res = 0;
  for (int b = 4; b <= n; b++) {
    g = t - b;
    if (g < 1) {
      continue;
    }
    res += C(n, b) * C(m, g);
  }
  printf("%.0Lf", res);
}
