#include <bits/stdc++.h>
using namespace std;
long long res;
long long fact(long long n) {
  if (n <= 1) return 1;
  return fact(n - 1) * n;
}
long long C(long long n, long long r) {
  if (r > n) return 0;
  if (r * 2 > n) r = n - r;
  if (r == 0) return 1;
  long long ret = n;
  for (int i = 2; i <= r; ++i) {
    ret *= (n - i + 1);
    ret /= i;
  }
  return ret;
}
void comp(long long b, long long g, long long tot) {
  for (int i = 4; i <= tot; i++) {
    long long fromB = C(b, i);
    long long fromG = C(g, tot - i);
    if (tot - i < 1) continue;
    res += fromB * fromG;
  }
}
int main() {
  long long b, g, tot;
  cin >> b >> g >> tot;
  comp(b, g, tot);
  cout << res << '\n';
  return 0;
}
