#include <bits/stdc++.h>
using namespace std;
int n, m, k;
long double lnfac[110000];
long double lnC(int n, int m) { return lnfac[n] - lnfac[m] - lnfac[n - m]; }
int main() {
  scanf("%d%d%d", &n, &m, &k);
  for (int i = 1; i <= m; i++) lnfac[i] = lnfac[i - 1] + log(i);
  long double ans = 0;
  for (int i = 0; i <= n; i++)
    for (int j = 0; j <= n; j++) {
      int num = (i + j) * n - i * j;
      if (num <= k) {
        long double lntmp =
            lnC(n, i) + lnC(n, j) + lnC(m - num, k - num) - lnC(m, k);
        ans += exp(lntmp);
        if (ans > 1e99) {
          ans = 1e99;
          break;
        }
      }
    }
  printf("%.12lf\n", (double)ans);
  return 0;
}
