#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 3;
long double f[N];
long double c(int n, int m) { return f[n] - f[m] - f[n - m]; }
int main() {
  int n, m, i, j, k, o;
  long double ans = 0;
  scanf("%d%d%d", &n, &m, &k);
  for (i = 1; i <= m; ++i) f[i] = f[i - 1] + log((long double)i);
  for (i = 0; i <= n; ++i)
    for (j = 0; j <= n; ++j) {
      o = n * (i + j) - i * j;
      if (o <= k) ans += exp(c(n, i) + c(n, j) + c(m - o, k - o) - c(m, k));
    }
  if (ans < 1e99)
    printf("%.13Lg", ans);
  else
    puts("1e99");
  return 0;
}
