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();
    if((4*B-5*A>=5)||(5*A-4*B>=4)){System.out.println(-1);}
    else{if(5*A-4*B<=0){System.out.println(10*B);}
    else{ int C=25*A%2;
         System.out.println((25*A+C)/2);}
        }
  }
}
/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