#include <bits/stdc++.h>
using namespace std;
void give(long long int arr[], long long int x) {
  for (long long int i = 1; i <= x; i++) {
    arr[i] = arr[i - 1] * (x - i + 1);
    arr[i] /= i;
  }
}
int main() {
  long long int n, m, t, sum = 0;
  cin >> n >> m >> t;
  long long int arr1[n + 1], arr2[m + 1];
  arr1[0] = 1;
  arr2[0] = 1;
  give(arr1, n);
  give(arr2, m);
  long long int a = t - 1, b = 1;
  while (a >= 4) {
    if (a <= n and a >= 4 and b >= 1 and b <= m) {
      long long int p = arr1[a] * arr2[b];
      sum += p;
    }
    a--;
    b++;
  }
  cout << sum << endl;
}
