import java.util.*;
public class Main {
    public static void main(String [] args){
        Scanner sc = new Scanner(System.in);
        int A = sc.nextInt();
        int B = sc.nextInt();
        boolean check = false;
        for(int i=1;i<=1009;i++){
            if(Math.floor(i*0.08)==A&&Math.floor(i*0.1)==B){
                System.out.println(i);
                check = true;
                break;
            }
        }
        if(!check) 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