#include <bits/stdc++.h>
using namespace std;
int main() {
  long long int i, j, n, m, t, p, ans = 0;
  cin >> n >> m >> t;
  long long int arr[33][33];
  for (i = 0; i <= 30; i++) {
    for (j = 0; j <= 30; j++) {
      arr[i][j] = 0;
    }
  }
  for (j = 0; j <= n; j++) {
    arr[j][0] = 1;
  }
  for (i = 1; i <= 32; i++) {
    for (j = 1; j <= i; j++) {
      arr[i][j] = arr[i - 1][j - 1] + arr[i - 1][j];
    }
  }
  for (i = 4; i <= n; i++) {
    p = t - i;
    if (i < t && p <= m) ans += (arr[n][i] * arr[m][p]);
  }
  cout << ans;
}
