#include <bits/stdc++.h>
using namespace std;
long long int dp[100][100];
int main() {
  dp[0][0] = 0;
  dp[0][1] = 1;
  dp[1][1] = 1;
  for (int i = 0; i <= 30; i++) {
    for (int j = 0; j <= 30; j++) {
      if (j == 0 || i == j)
        dp[i][j] = 1;
      else
        dp[i][j] = dp[i - 1][j] + dp[i - 1][j - 1];
    }
  }
  long long int n, m, t, sum = 0;
  cin >> n >> m >> t;
  for (int i = 4; i < t; i++) {
    int g = t - i;
    sum += dp[n][i] * dp[m][g];
  }
  cout << sum;
}
