#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int n, m, t;
  cin >> n >> m >> t;
  if (t > m + n || n < 4 || m < 1) {
    cout << "0";
    return 0;
  }
  long long int ans = 0;
  long long int b[31][31] = {0};
  for (int i = 0; i < 31; i++) {
    b[i][i] = 1;
    b[i][0] = 1;
  }
  for (int i = 2; i < 31; i++) {
    for (int r = 1; r < i; r++) {
      b[i][r] = b[i - 1][r - 1] + b[i - 1][r];
    }
  }
  for (int i = 4; i <= n; i++) {
    if ((t - i < 1) || (t - i > m)) {
      continue;
    }
    ans += b[n][i] * b[m][t - i];
  }
  cout << ans;
}
