#include <bits/stdc++.h>
using namespace std;
const int M = 100 * 1000 + 20;
const long double inf = 1e99;
int n, m, k;
long double fact[M], ans;
long double c(int a, int b) { return fact[a] - fact[b] - fact[a - b]; }
int main() {
  ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
  cin >> n >> m >> k;
  fact[0] = log(1);
  for (int i = 1; i < M; i++) fact[i] = fact[i - 1] + log(i);
  for (int i = 0; i <= n; i++)
    for (int j = 0; j <= n; j++) {
      int l = (i + j) * n - i * j;
      if (l <= k)
        ans =
            min(inf, ans + exp(c(n, i) + c(n, j) + c(m - l, k - l) - c(m, k)));
    }
  return cout << setprecision(10) << fixed << ans << endl, 0;
}
