#include <iostream>
#include <algorithm>
#include <vector>
#include <map>
#include <cmath>

using namespace std;

int main() {
  int F, N, K;
  cin >> F >> N >> K;

  double ans = 0;

  for (int t = 1; t <= F; t++) {
    static double dp0[101][101];
    static double dp1[101][101];
    fill_n(*dp0, 101 * 101, 0.0);
    dp0[0][0] = 1;

    for (int k = 0; k < N; k++) {
      fill_n(*dp1, 101 * 101, 0.0);
      for (int i = 0; i <= k; i++) {
        for (int j = 0; i + j <= k; j++) {
          dp1[i + 1][j] += 1.0 * (F - t) / F * dp0[i][j];
          dp1[i][j + 1] += 1.0 / F * dp0[i][j];
          dp1[i][j] += 1.0 * (t - 1) / F * dp0[i][j];
        }
      }
      swap(dp0, dp1);
    }
    for (int i = 0; i <= N; i++) {
      for (int j = 0; i + j <= N; j++) {
        if (i + 1 <= K && K <= i + j) {
          ans += t * dp0[i][j];
        }
      }
    }
  }
  printf("%.20f\n", ans);
}