
import java.util.Scanner;

/**
 * 增税
 */
public class Main {
    static Scanner sc = new Scanner(System.in);
    public static void main(String[] args) {
        int a = sc.nextInt();
        int b = sc.nextInt();

        int ans = -1;
        for (int i =0; i< 10009; i++){
            if((int) (i * 0.08) == a ){
                if((int) (i * 0.1) == 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