import java.util.*;
 
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        
        double a = sc.nextDouble();
        double b = sc.nextDouble();
        
        for(int i=1; i<=1250; i++){
            if(Math.floor(i*0.08)==a && Math.floor(i*0.1)==b){
                System.out.println(i);
                return;
            }
        }

        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