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 chi = 0;
        int s = -1;
        for(int i = 0 ; i <= 1000 && chi == 0; i++ ){
            int aa = (int)(i * 0.08);
            double bb = (int)(i * 0.1);
            if(a == aa && b == bb){
                chi = 1;
                s = i;
            }
        }
        System.out.println(s);
    }
}
/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