#include <bits/stdc++.h>
using namespace std;
unsigned long long C(int n, int m) {
  unsigned long long z = 1;
  for (int i = 0; i < m; i++) z = z * (n - i) / (i + 1);
  return z;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  unsigned long long n, m, t;
  cin >> n >> m >> t;
  unsigned long long ans = 0;
  for (int i = 1; i <= t - 4; i++) {
    int g = i;
    int b = t - i;
    ans += C(n, b) * C(m, g);
  }
  cout << ans;
  return 0;
}
