import java.util.Scanner;

public class Main{
 public static void main(String[] args) {
   Scanner kbd =new Scanner(System.in);
   int A=kbd.nextInt();
   int B=kbd.nextInt();
   int x=-1;
   for(int i=13;i<=1010;i++){
     double n=Math.floor(i*0.08);
     double m=Math.floor(i*0.1);
     if(A==n&&B==m){
       x=i;
       break;
     }
   }
    System.out.println(x);
 }
}


/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