#include <bits/stdc++.h>
using namespace std;
const long double lim = 1e99;
template <typename T>
inline T read() {
  register T sum = 0;
  register char cc = getchar();
  int sym = 1;
  while (cc != '-' && (cc > '9' || cc < '0')) cc = getchar();
  if (cc == '-') sym = -1, cc = getchar();
  sum = sum * 10 + cc - '0';
  cc = getchar();
  while (cc >= '0' && cc <= '9') sum = sum * 10 + cc - '0', cc = getchar();
  return sym * sum;
}
template <typename T>
inline T read(T& a) {
  a = read<T>();
  return a;
}
template <typename T, typename... Others>
inline void read(T& a, Others&... b) {
  a = read(a);
  read(b...);
}
int n, m, K;
long double ans, fac[100010];
long double C(int n, int m) { return fac[n] - fac[m] - fac[n - m]; }
int main() {
  read(n, m, K);
  for (int i = 1; i <= m; i++) fac[i] = fac[i - 1] + log(1. * i);
  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 p = C(n, i) + C(n, j) + C(m - num, K - num) - C(m, K);
        ans = min(ans + exp(p), lim);
      }
    }
  printf("%.15Lf\n", ans);
  return 0;
}
