#include <bits/stdc++.h>
using namespace std;
long long comb(long long n, int k) {
  long long res = 1;
  for (int i = 0; i < k; i++) res = (res * (n - i)) / (i + 1);
  return res;
}
int main() {
  long long n, m, t;
  cin >> n >> m >> t;
  long long res = 0;
  for (long long a = 4; a <= n; a++) {
    long long b = t - a;
    if (1 <= b && b <= m) {
      res += comb(n, a) * comb(m, b);
    }
  }
  cout << res << endl;
}
