#include <bits/stdc++.h>
using namespace std;
const double eps(1e-8);
int n, m, k;
long double g[100010];
long double calc(int n, int m) {
  long double ret = 0;
  ret = g[n] - g[m] - g[n - m];
  return ret;
}
int main() {
  g[0] = 0;
  for (int i = 1; i <= 100000; i++) g[i] = g[i - 1] + log(i * 1.0);
  scanf("%d%d%d", &n, &m, &k);
  long double ret = 0;
  for (int i = 0; i <= n; i++)
    for (int j = 0; j <= n; j++)
      if (i * n + j * n - i * j <= k) {
        int sum = i * n + j * n - i * j;
        long double tmp =
            calc(n, i) + calc(n, j) + calc(m - sum, k - sum) - calc(m, k);
        ret = min((long double)1e99, ret + exp(tmp));
      }
  printf("%.10f\n", (double)ret);
  return 0;
}
