#include <bits/stdc++.h>
long double fac[100005];
inline long double binom(int n, int m) { return fac[n] - fac[n - m] - fac[m]; }
int main() {
  int n, m, k;
  long double ans = 0.00;
  scanf("%d%d%d", &n, &m, &k);
  for (register int i = 1; i <= m; ++i) fac[i] = fac[i - 1] + log(1.00 * i);
  for (register int r = 0; r <= n; ++r) {
    for (register int c = 0; c <= n; ++c) {
      int t = (r + c) * n - r * c;
      if (k >= t)
        ans +=
            exp(binom(n, r) + binom(n, c) + binom(m - t, k - t) - binom(m, k));
    }
  }
  if (ans > 1e99)
    printf("%.10lf\n", (double)1e99);
  else
    printf("%.10lf", (double)ans);
  return 0;
}
