#include <bits/stdc++.h>
using namespace std;
long long int arr[300][300];
void precal() {
  arr[0][0] = 1;
  for (int i = 1; i < 32; ++i) {
    arr[i][0] = 1;
    for (int j = 1; j <= i; ++j) {
      arr[i][j] = (arr[i - 1][j] + arr[i - 1][j - 1]);
    }
  }
}
int main() {
  precal();
  int t, m, n;
  cin >> t >> m >> n;
  long long int sum = 0;
  for (int i = 4; i < n; ++i) {
    sum += (arr[t][i] * arr[m][n - i]);
  }
  cout << sum;
  return 0;
}
