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