#include <bits/stdc++.h>
using namespace std;
unsigned long long dp[31][31];
unsigned long long solve(unsigned long long n, unsigned long long r) {
  if (n == r) return 1;
  if (r == 1) return n;
  unsigned long long &ret = dp[n][r];
  if (ret != -1) return ret;
  return ret = solve(n - 1, r) + solve(n - 1, r - 1);
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  unsigned long long n, m, t, ans = 0;
  cin >> n >> m >> t;
  vector<pair<unsigned long long, unsigned long long> > V;
  unsigned long long b, g;
  if (n >= t) {
    b = t - 1, g = 1;
  } else {
    b = n, g = t - n;
  }
  while (b >= 4) {
    if (b + g <= t && b <= n && g <= m) V.push_back({b, g});
    b--, g++;
  }
  for (int i = 0; i < V.size(); i++) {
    memset(dp, -1, sizeof dp);
    unsigned long long a = solve(n, V[i].first);
    memset(dp, -1, sizeof dp);
    unsigned long long b = solve(m, V[i].second);
    ans += (a * b);
  }
  cout << ans << endl;
  return 0;
}
