#include <bits/stdc++.h>
using namespace std;
long long c(long long x, long long y) {
  if (y == 0) return 1;
  return x * c(x - 1, y - 1) / y;
}
int main() {
  ios_base::sync_with_stdio(0);
  int n, m, t;
  cin >> n >> m >> t;
  long long s = 0;
  for (int i = 4; i < t; ++i) {
    s += c(n, i) * c(m, t - i);
  }
  cout << s;
}
