#include <bits/stdc++.h>
using namespace std;
long double add(long double a, long double b) {
  a += b;
  if (a > 1e99) a = 1e99;
  return a;
}
long double f[100010];
int n, m, k;
long double C(int a, int b) { return f[a] - f[b] - f[a - b]; }
int main() {
  scanf("%d%d%d", &n, &m, &k);
  f[0] = 0;
  for (int i = 1; i <= 100000; i++) f[i] = f[i - 1] + log(i);
  long double ans = 0;
  for (int i = 0; i <= n; i++) {
    for (int j = 0; j <= n; j++) {
      if (n * (i + j) - i * j <= k) {
        int z = n * (i + j) - i * j;
        long double tmp = C(n, i) + C(n, j) + C(m - z, k - z) - C(m, k);
        ans = add(ans, exp(tmp));
      }
    }
  }
  printf("%.10lf\n", (double)ans);
  return 0;
}
