import java.util.*;
 
public class Main {
 
    public static void main(String[] args) {
        Scanner stdIn = new Scanner(System.in);
        int A = stdIn.nextInt();
        int B = stdIn.nextInt();
        stdIn.close();

        int result = 0;
        for (int i = 13; i <= 1000; i++) {
            if (((int)Math.floor(i * 0.08) == A) && ((int)Math.floor(i * 0.1) == B)) {
                System.out.println(i);
                result = 1;
                break;
            }
        }   
        if (result == 0) {
            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