#include <bits/stdc++.h>
using namespace std;
const int MAXN = 30;
long long C[MAXN + 1][MAXN + 1];
int main() {
  int n, m, k, t, b, lim;
  long long ans = 0LL;
  for (n = 0; n <= MAXN; ++n) {
    C[n][0] = C[n][n] = 1LL;
    for (k = 1; k < n; ++k) C[n][k] = C[n - 1][k - 1] + C[n - 1][k];
  }
  scanf("%d%d%d", &n, &m, &t);
  lim = min(t - 1, n);
  for (b = max(4, t - m); b <= lim; ++b) ans += C[n][b] * C[m][t - b];
  printf("%I64d\n", ans);
  return 0;
}
