#include <bits/stdc++.h>
using namespace std;
unsigned long long B[31][31], res = 0;
int main(void) {
  for (int i = 0; i <= 30; i++) {
    B[i][0] = B[i][i] = 1;
    for (int j = 1; j < i; j++) B[i][j] = B[i - 1][j - 1] + B[i - 1][j];
  }
  int n, m, k;
  cin >> n >> m >> k;
  for (int b = 4; b < k; b++) {
    res += (b <= n && k - b <= m) ? B[n][b] * B[m][k - b] : 0;
  }
  cout << res;
  return 0;
}
