import java.util.Scanner;

public class Main {
	 
    /**
     * @param args
     */
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		int b = sc.nextInt();
		double get = (double)((a-1)*2.5+1.5*b);
		System.out.println( String.format("%.1f", get));
		
	}
	public static void printArr(int [] a){
		for (int i = 0 ;i<= a.length - 1 ;i++) {
			System.out.print( a[i] + " ");
		}
	}
}
/**************************************************************
	Problem: 1603
	User: admin
	Language: Java
	Result: Accepted
	Time:794 ms
	Memory:40616 kb
****************************************************************/