#include <bits/stdc++.h>
using namespace std;
int n, m, k;
double ncr[305][305];
double prob[100000];
int main() {
  for (int i = 0; i <= 302; i++) ncr[i][0] = 1.0;
  for (int i = 1; i <= 302; i++)
    for (int j = 1; j <= i; j++) ncr[i][j] = ncr[i - 1][j] + ncr[i - 1][j - 1];
  cin >> n >> m >> k;
  prob[0] = 1.0;
  for (int i = 1; i <= n * n + 2; i++) {
    prob[i] = prob[i - 1] * (double)(k - i + 1) / (double)(m - i + 1);
  }
  double anss = 0.0;
  for (int i = 0; i <= n; i++) {
    for (int j = 0; j <= n; j++) {
      int hoise = i * n + j * n - i * j;
      double tmp = ncr[n][i] * ncr[n][j] * prob[hoise];
      anss += tmp;
      if (anss > 1e99) {
        cout << 1e99 << endl;
        return 0;
      }
    }
  }
  printf("%0.10lf\n", anss);
  return 0;
}
