#include <bits/stdc++.h>
using namespace std;
long fact(long n) {
  long s = 1, i;
  for (i = 1; i <= n; i++) s *= i;
  return s;
}
long long nCr(int n, int m) {
  int k;
  register int i, j;
  long long c, d;
  c = d = 1;
  k = (m > (n - m)) ? m : (n - m);
  for (j = 1, i = k + 1; (i <= n); i++, j++) {
    c *= i;
    d *= j;
    if (!fmod(c, d) && (d != 1)) {
      c /= d;
      d = 1;
    }
  }
  return c;
}
int main() {
  long a, b, c, i, j;
  while (scanf("%ld %ld %ld", &a, &b, &c) == 3) {
    long long res = 0;
    for (i = 4; i <= a; i++) {
      for (j = 1; j <= b; j++)
        if (i + j == c) {
          res += nCr(a, i) * nCr(b, j);
        }
    }
    cout << res << endl;
  }
  return 0;
}
