#include <bits/stdc++.h>
using namespace std;
long long int dp[31][31];
void compute() {
  for (int i = 1; i <= 30; i++) {
    dp[i][1] = i;
    dp[i][i] = 1;
  }
  for (int i = 1; i <= 30; i++) {
    for (int j = 2; j < i; j++) {
      dp[i][j] = dp[i - 1][j] + dp[i - 1][j - 1];
    }
  }
}
int main() {
  compute();
  int n, m, t;
  cin >> n >> m >> t;
  int64_t ans = 0;
  for (int i = 4; i <= n; i++) {
    if (t - i <= m && t - i >= 1) {
      ans += dp[n][i] * dp[m][t - i];
    }
  }
  cout << ans << "\n";
}
