package no023;

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		double p = 0;
		double x = 2/3D;
		for(int i=1;i<=100;i++) {
			p += x * i;
			x /= 3;
		}
		Scanner sc = new Scanner(System.in);
		int h = sc.nextInt();
		int a = sc.nextInt();
		int d = sc.nextInt();
		double[] dp = new double[h+1];
		for(int i=1;i<=h;i++) {
			if (i <= a) {
				dp[i] = 1;
			}else{
				dp[i] = Math.min(dp[i-a]+1,dp[Math.max(i-d,0)]+p);
			}
		}
		System.out.println(dp[h]);
	}

}