import java.util.*;
import java.io.*;
public class Main{
  
    public static void main(String [] args){
        Scanner sc=new Scanner(System.in);
        int a=sc.nextInt();
        int b=sc.nextInt();
        boolean found=false;
        for(int i=1;i<=10000;i++){

            if(((i*8)/100)==a && ((i*10)/100)==b){
                found=true;
                System.out.println(i+" ");
                break;
            }
        }
        if(!found){
            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