#include <bits/stdc++.h>
using namespace std;
long long int ncr(long long int n, long long int r) {
  long long int num = 1;
  for (int i = 1; i <= r; i++) {
    num *= n - i + 1;
    num /= i;
  }
  return num;
}
int main() {
  long long int a, b, t, sum = 0;
  cin >> a >> b >> t;
  for (long long int i = 4; i <= t - 1; i++) sum += ncr(a, i) * ncr(b, t - i);
  cout << sum;
  return 0;
}
