#include <bits/stdc++.h>
using namespace std;
long long comb(int, int);
int main() {
  int b, b1, g, g1, t;
  long long res, sum = 0;
  ;
  cin >> b >> g >> t;
  b1 = 4;
  g1 = t - b1;
  while (g1 >= 1) {
    res = comb(b, b1);
    res *= comb(g, g1);
    sum += res;
    b1++;
    g1--;
  }
  cout << sum << endl;
  return 0;
}
long long comb(int n, int r) {
  long long res = 1;
  for (int i = 1; i <= r; i++) {
    res *= n;
    res /= i;
    n--;
  }
  return res;
}
