#include <bits/stdc++.h>
using namespace std;
long long int combine(int n, int r) {
  long long int sum = 1;
  for (int i = 1; i <= r; i++) {
    sum *= n - i + 1;
    sum /= i;
  }
  return sum;
}
int main() {
  int x, y, c;
  cin >> x >> y >> c;
  long long int sum = 0;
  for (int i = 4; i < c; i++) {
    sum += combine(x, i) * combine(y, c - i);
  }
  cout << sum << endl;
}
