#include <bits/stdc++.h>
using namespace std;
const int mxn = 1e5 + 1;
long long ncr(long long n, long long r) {
  long long ans = 1;
  long long i;
  for (i = 0; i < r; i++) {
    ans = ans * (n - i) / (i + 1);
  }
  return ans;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long t = 1;
  while (t--) {
    long long n, m, t, ans = 0, boy, girl;
    cin >> n >> m >> t;
    for (boy = 4; boy < n + 1; boy++) {
      girl = t - boy;
      if (girl < 1) break;
      if (girl > m) continue;
      long long himj = ncr(n, boy) * ncr(m, girl);
      ans += himj;
    }
    cout << ans;
  }
  return 0;
}
