#include <bits/stdc++.h>
using namespace std;
long long A[1000000];
long long ncr(int n, int k) {
  long long ans = 1;
  k = k > n - k ? n - k : k;
  int j = 1;
  for (; j <= k; j++, n--) {
    if (n % j == 0) {
      ans *= n / j;
    } else if (ans % j == 0) {
      ans = ans / j * n;
    } else {
      ans = (ans * n) / j;
    }
  }
  return ans;
}
int main() {
  ios::sync_with_stdio(false);
  long long n, m, t;
  cin >> n >> m >> t;
  long long sum = 0;
  for (long long i = 4; i <= n; i++)
    for (long long j = 1; j <= m; j++)
      if (i + j == t) sum += ncr(n, i) * ncr(m, j);
  cout << sum << endl;
  return 0;
}
