#include <bits/stdc++.h>

using namespace std;

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int f, n, k;
  cin >> f >> n >> k;

  double ret = 0;
  for (int x = 1; x <= f; x++) {
    vector<double> dp(n+1);   // dp[i]: x以上がn回中i回でる確率
    dp[0] = 1;
    for (int i = 0; i < n; i++) {
      for (int j = n; j >= 0; j--) {
        double p = (f - x + 1.0) / f;
        dp[j] *= 1 - p;
        if (j > 0)
          dp[j] += p * dp[j-1];
      }
    }
    for (int i = k; i <= n; i++)
      ret += dp[i];
  }

  cout << fixed << setprecision(12) << ret << endl;
  
  return 0;
}