#include <bits/stdc++.h>
const int N = 100010;
int n, m, k;
long double f[N], ans;
inline long double C(int n, int m) { return f[n] - f[m] - f[n - m]; }
int main() {
  scanf("%d%d%d", &n, &m, &k);
  for (int i = 1; i <= m; ++i) f[i] = f[i - 1] + log(i);
  for (int i = 0; i <= n; ++i)
    for (int x, j = 0; j <= n; ++j) {
      x = (i + j) * n - i * j;
      if (x <= k)
        ans = std::min(
            1e99L, ans + exp(C(n, i) + C(n, j) + C(m - x, k - x) - C(m, k)));
    }
  printf("%.10lf", (double)ans);
}
