#include <bits/stdc++.h>
const int INF = 0x3f3f3f3f, MOD = 1e9 + 7;
using namespace std;
long long c(long long a, long long b) {
  long long res = 1;
  for (long long i = 1; i <= b; i++) {
    res *= a - i + 1;
    res /= i;
  }
  return res;
}
int main() {
  ios::sync_with_stdio(false);
  long long n, m, t;
  cin >> n >> m >> t;
  long long res = 0;
  for (long long b = 1; b <= t - 4; b++) {
    res += c(m, b) * c(n, t - b);
  }
  cout << res;
  return 0;
}
