#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 5;
int n, m, k;
long double fact[N];
long double ans;
long double c(int a, int b) { return fact[a] - fact[b] - fact[a - b]; }
int main() {
  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  cout << fixed << setprecision(10);
  cin >> n >> m >> k;
  fact[0] = 0;
  for (int i = 1; i < N; i++) fact[i] = fact[i - 1] + (long double)log(i);
  for (int i = 0; i <= n; i++) {
    for (int j = 0; j <= n; j++) {
      int T = (i + j) * n - (i * j);
      if (T > k) continue;
      ans += exp(c(n, i) + c(n, j) + c(m - T, k - T) - c(m, k));
      if (ans > 1e99)
        return cout << "1e99"
                    << "\n",
               0;
    }
  }
  cout << ans << "\n";
}
