import java.util.Scanner;

public class Main2 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int H = scanner.nextInt();
        int A = scanner.nextInt();
        int D = scanner.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)] + 3.0 / 2);
            }
        }
        System.out.println(dp[H]);
    }
}