#include <bits/stdc++.h>
using namespace std;
bool isPrime(unsigned long long int n) {
  if (n <= 1) return true;
  if (n <= 3) return true;
  if (n % 2 == 0 || n % 3 == 0) return false;
  for (unsigned long long int i = 5; i * i <= n; i = i + 6)
    if (n % i == 0 || n % (i + 2) == 0) return false;
  return true;
}
long long int pow(long long int a, long long int b, long long int m) {
  long long int res = 1;
  while (b > 0) {
    if (b & 1) res = (res * a) % m;
    a = (a * a) % m;
    b >>= 1;
  }
  return res;
}
long long int ncr(int n, int k) {
  if (k > n) return 0;
  long long int res = 1;
  if (k > n - k) k = n - k;
  for (int i = 0; i < k; ++i) {
    res *= (n - i);
    res /= (i + 1);
  }
  return res;
}
void solve() {
  int n, m, t;
  cin >> n >> m >> t;
  int b = 4;
  long long int ans = 0;
  while (t - b >= 1) {
    ans += ncr(n, b) * ncr(m, t - b);
    b++;
  }
  cout << ans << endl;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  long long int t = 1;
  while (t--) {
    solve();
  }
}
