#include <bits/stdc++.h>
using namespace std;
double f[100010];
double C[310][310];
int main(void) {
  int N, M, K, i, j;
  cin >> N >> M >> K;
  f[0] = 1.0;
  for ((i) = 0; (i) < (int)(K); (i)++) f[i + 1] = f[i] * (K - i) / (M - i);
  for ((i) = 0; (i) < (int)(N + 1); (i)++)
    for ((j) = 0; (j) < (int)(i + 1); (j)++) {
      if (j == 0 || j == i)
        C[i][j] = 1;
      else
        C[i][j] = C[i - 1][j - 1] + C[i - 1][j];
    }
  double INF = 1.0E+99;
  double ans = 0.0;
  for ((i) = 0; (i) < (int)(N + 1); (i)++)
    for ((j) = 0; (j) < (int)(N + 1); (j)++)
      ans = min(INF, ans + f[i * N + j * N - i * j] * C[N][i] * C[N][j]);
  printf("%.12f\n", ans);
  return 0;
}
