#include <bits/stdc++.h>
using namespace std;
const int N = 40;
int n, m, t;
long long ncr[N][N] = {0};
int main() {
  for (int i = (0); i < (int)(N); i++) ncr[i][0] = 1;
  for (int i = (1); i < (int)(N); i++)
    for (int j = (1); j <= (int)(i); j++)
      ncr[i][j] = ncr[i - 1][j] + ncr[i - 1][j - 1];
  cin >> n >> m >> t;
  long long ans = 0;
  for (int i = (0); i <= (int)(t); i++) {
    int j = t - i;
    if (i <= n && j <= m && i >= 4 && j >= 1) {
      ans += ncr[n][i] * ncr[m][j];
    }
  }
  cout << ans << endl;
  return 0;
}
