#include <bits/stdc++.h>
using namespace std;
long long l[31][31] = {0};
void ncrvalue() {
  int i, j;
  l[0][0] = 1;
  for (i = 1; i <= 30; i++) {
    l[i][0] = 1;
    for (j = 1; j < i + 1; j++) l[i][j] = l[i - 1][j - 1] + l[i - 1][j];
  }
}
int main() {
  long long n, m, t, i, ans, j;
  cin >> n >> m >> t;
  ncrvalue();
  vector<long long> v;
  for (i = 4; i <= n; i++) {
    if (t - i >= 1 && t - i <= m) v.push_back(i);
  }
  ans = 0;
  for (i = 0; i < v.size(); i++) ans = ans + (l[n][v[i]] * l[m][t - v[i]]);
  cout << ans << endl;
}
