import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        long A = sc.nextInt();
        long B = sc.nextInt();

        for(int i = 10; i < 1010; i++) {
            if((int)(i * 0.08) == A && (int)(i*0.1) == B) {
                System.out.println(i);
                return;
            }
        }
        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