#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 10, M = 998244353;
long long fac[N];
int b, g, n;
long long chose(int n, int r) {
  long long re = 1;
  long long f = fac[min(n - r, r)];
  for (int i = n; i > max(n - r, r); --i) {
    if (f % i == 0)
      f /= i;
    else
      re *= i;
  }
  return (re / f);
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  fac[0] = 1;
  for (int i = 1; i <= 15; ++i) fac[i] = fac[i - 1] * i;
  cin >> b >> g >> n;
  long long ans = 0;
  for (int i = 4; i <= b; ++i) {
    if (n - i <= g && n - i >= 1) {
      ans += chose(b, i) * chose(g, n - i);
    }
  }
  cout << ans << endl;
  return 0;
}
