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();
        int price = 0;
        boolean judge = false;
        
        for(int i=1; i<=1000; i++){
            price = i;
            if(Math.floor(price*0.08) == A && Math.floor(price*0.1) == B){
                judge = true;
                break;
            }
        }
        
        if(judge) System.out.println(price);
        else 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