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