import java.util.Scanner;

public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int first_num = sc.nextInt();
        int second_num = sc.nextInt();
        for(int i = 1;i < 2000 ;i++){
            if(Math.floor(i*0.08) == first_num && Math.floor(i*0.1) == second_num){
                System.out.println(i);
                System.exit(0);
            }
        }
        System.out.println(-1);
    }
}
/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