import java.math.*;
import java.util.*;
class Main{
    public static void main(String[] args){
        Scanner sc=new Scanner(System.in);
        double a = sc.nextInt();
        double b = sc.nextInt();
        double ans =-1d;
        outloop: for(double i = 1.0;i<=1009.0;i=i+1.0){
            double ia =Math.floor(i*0.08);
            double ib =Math.floor(i*0.1);
            if(ia==a&&ib==b){
                ans =i;
                break outloop;
            }
            }
            int an =(int)ans;
            System.out.println(an);
        }
	}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz