#include <bits/stdc++.h>
using namespace std;
int N, M, K;
long double f[1 << 17], ans;
long double lncr(int a, int b) { return f[a] - f[b] - f[a - b]; }
long double res(int r, int c) {
  int v = r * c - N * r - N * c;
  if (K + v < 0) return 0;
  return exp(lncr(N, r) + lncr(N, c) + lncr(M + v, K + v) - lncr(M, K));
}
int main() {
  for (int i = 1; i < 1 << 17; i++) f[i] = f[i - 1] + log(i);
  cin >> N >> M >> K;
  for (int r = 0; r <= N; r++)
    for (int c = 0; c <= N; c++) ans += res(r, c);
  cout.precision(20);
  if (ans > 1e99)
    cout << "1e99" << endl;
  else
    cout << ans << endl;
  return 0;
}
