import java.util.Scanner;
 
public class Main {
	public static void main(String[] args) {
		Main p = new Main();
	}
	double c, prob;
 
	public Main() {
		Scanner sc = new Scanner(System.in);
		int h = sc.nextInt();
		int a = sc.nextInt();
		int d = sc.nextInt();
 
		c = 1.0; prob = 0.0;
		for(int i=0;i<200;i++){
			prob += 1*c;
			c /= 3.0;
		}
 
		solve(h, a, d);
	}
 
	public void solve(int h, int a, int d) {
 
		double res = (h-1)/a+1;
		int m = (h-1)/a + 1;
		for(int i=0;i<=m;i++){
			res = Math.min(res, i+((h-i*a-1)/d+1)*prob);
		}
 
		System.out.println(res);
	}
 
}