#include <bits/stdc++.h>
using namespace std;
const long long INF = 0x3f3f3f3f;
const int N = 1e5 + 10;
const long long mod = 998244353;
const bool debug = false;
long double F[N];
void init() {
  for (int i = 1; i < N; ++i) F[i] = F[i - 1] + logl(i);
}
long double comb(int n, int m) { return F[n] - F[m] - F[n - m]; }
int main() {
  init();
  int n, m, k;
  scanf("%d%d%d", &n, &m, &k);
  long double ans = 0, tmp;
  for (int i = 0; i <= n; ++i) {
    for (int j = 0; j <= n; ++j) {
      int t = (i + j) * n - i * j;
      if (t <= k) {
        tmp = comb(n, i) + comb(n, j) + comb(m - t, k - t) - comb(m, k);
        ans = min((long double)1e99, ans + expl(tmp));
      }
    }
  }
  cout << setprecision(18);
  cout << ans;
  return 0;
}
