#include <bits/stdc++.h>
using namespace std;
long long int pascal[31][31];
int main(void) {
  int n, m, t;
  cin >> n >> m >> t;
  pascal[0][0] = 1;
  pascal[1][0] = pascal[1][1] = 1;
  for (int i = 2; i <= 30; i++) {
    pascal[i][0] = 1;
    for (int j = 1; j < i; j++) {
      pascal[i][j] = (pascal[i - 1][j - 1] + pascal[i - 1][j]);
    }
    pascal[i][i] = 1;
  }
  long long int tot = 0;
  for (int cm = 4; cm <= min(t, n); cm++) {
    int cw = t - cm;
    if (t - cm <= m && cw >= 1) {
      tot += (pascal[n][cm] * pascal[m][cw]);
    }
  }
  cout << tot << endl;
  return 0;
}
