#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 2 * 1e5 + 10;
const int mod = 1e9 + 7;
ll res;
ll a[N];
ll fact[N];
ll invfact[N];
void pre() {
  fact[0] = invfact[0] = invfact[1] = 1;
  for (int i = 1; i < N; ++i) {
    fact[i] = (fact[i - 1] * i) % mod;
  }
  for (int i = 2; i < N; ++i) {
    invfact[i] = (mod - mod / i) * invfact[mod % i] % mod;
  }
  for (int i = 1; i < N; ++i) {
    invfact[i] = (invfact[i - 1] * invfact[i]) % mod;
  }
}
ll nCr(ll n, ll r) {
  return (((fact[n] * invfact[r]) % mod) * invfact[n - r]) % mod;
}
void solve() {
  ll n, m, t;
  cin >> n >> m >> t;
  for (int i = 4; i < t; ++i) {
    if (i <= n && t - i <= m) {
      res += nCr(n, i) * nCr(m, t - i);
    }
  }
  cout << res;
}
int main(int argc, char const *argv[]) {
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  cout.tie(NULL);
  ll t = 1;
  pre();
  while (t--) {
    solve();
  }
}
