#include <bits/stdc++.h>
using namespace std;
long long int comb(long long int n, long long int r) {
  long long int C[r + 1];
  memset(C, 0, sizeof(C));
  C[0] = 1;
  for (long long int i = 1; i <= n; i++) {
    for (long long int j = min(i, r); j > 0; j--) C[j] = (C[j] + C[j - 1]);
  }
  return C[r];
}
long long int mod = 1e9 + 7;
int main() {
  long long int a, b, c, x = 0, i;
  cin >> a >> b >> c;
  for (i = 1; i <= c; i++) {
    if (c - i >= 4) x += comb(a, c - i) * comb(b, i);
  }
  cout << x;
}
