#include <bits/stdc++.h>
using namespace std;
long long Com(long long n, long long r) {
  if (r < 0 || r > n) return 0;
  long long res = 1, i = 0;
  while (i < r) ++i, res *= n - i + 1, res /= i;
  return res;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int n, m, t, f, s;
  long long ans = 0;
  cin >> n >> m >> t;
  f = t - 1;
  s = 1;
  while (f >= 4 && s <= m) {
    ans += Com(n, f) * Com(m, s);
    f--;
    s++;
  }
  cout << ans;
}
