#include <bits/stdc++.h>
using namespace std;
long long i, j, n, ss, m, p, a, b, c, u, v, t;
long long z;
int main() {
  scanf("%lld%lld%lld", &a, &b, &t);
  for (i = 4; i < t; i++)
    for (j = 1; j < t; j++) {
      if (i + j != t || i > a || j > b) continue;
      m = 1;
      v = 1;
      for (z = 1, u = a; z <= i; u--, z++) {
        m = m * u, v = v * z;
        if (m % v == 0) m /= v, v = 1;
      }
      p = m;
      m = 1;
      v = 1;
      for (z = 1, u = b; z <= j; u--, z++) {
        m = m * u, v = v * z;
        if (m % v == 0) m /= v, v = 1;
      }
      ss += (p * m);
    }
  printf("%lld\n", ss);
}
