#include <bits/stdc++.h>
using namespace std;
const int INF = 0x3f3f3f3f, maxn = 100001;
long long C(int n, int m) {
  long long ans = 1;
  for (int i = 1; i <= m; i++) ans = ans * (n - m + i) / i;
  return ans;
}
int main() {
  int n, m, t;
  while (~scanf("%d%d%d", &n, &m, &t)) {
    long long ans = 0;
    for (int i = 4; i <= n; i++)
      if (i < t && t - i <= m) ans += C(n, i) * C(m, t - i);
    printf("%I64d\n", ans);
  }
  return 0;
}
