#include <bits/stdc++.h>
using namespace std;
inline int read() {
  int x = 0, f = 1;
  char c = getchar();
  while (c < '0' || c > '9') {
    if (c == '-') f = -1;
    c = getchar();
  }
  while (c >= '0' && c <= '9') {
    x = (x << 3) + (x << 1) + c - '0';
    c = getchar();
  }
  return x * f;
}
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() {
  n = read(), m = read(), k = read();
  for (int i = 1; i <= m; ++i) {
    fac[i] = fac[i - 1] + log(i * 1.0);
  }
  for (int i = 0; i <= n; ++i) {
    for (int j = 0; j <= n; ++j) {
      int x = n * (i + j) - i * j;
      if (x > k) break;
      ans = min(ans + exp(C(n, i) + C(n, j) + C(k, x) - C(m, x)), 1e99L);
    }
  }
  if (ans >= 1e99) {
    printf("1e99\n");
    return 0;
  }
  double myh = ans;
  printf("%.10lf\n", myh);
  return 0;
}
