import java.util.Scanner;
public class Main{
  public static void main(String[] args){
  Scanner sc = new Scanner(System.in);
    int a = sc.nextInt();
    int b = sc.nextInt();
    int ans = -1;
    int ax;
    int bx;
    for(int i = 1; i <= 1000; i++){
       ax = (int) (i*0.08);
       bx = (int) (i*0.1);
       if(ax == a && bx == b){
         ans = i;
         break;
       }
    }
    System.out.println(ans);
  }
}
/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