#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 5;
int n, m, k;
long double ans, fc[N];
inline double C(int n, int m) { return fc[n] - fc[m] - fc[n - m]; }
int main() {
  scanf("%d%d%d", &n, &m, &k);
  for (int i = 1; i <= m; ++i) fc[i] = fc[i - 1] + log(1.0 * i);
  for (int i = 0; i <= n; ++i)
    for (int j = 0; j <= n; ++j) {
      int rc = n * (i + j) - i * j;
      if (rc > k) continue;
      ans += exp(C(n, i) + C(n, j) + C(m - rc, k - rc) - C(m, k));
    }
  printf("%.10f", min(1e99, (double)ans));
  return 0;
}
