
import java.util.Scanner;

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

        int roop = 0;
        // 最小から求める
        while (roop < 10000) {
            if (Math.floor((double) roop * 0.08) == a && Math.floor((double) roop * 0.1) == b) {
                System.out.println(roop);
                break;
            }
            roop++;
        }

        if (roop == 10000) {
            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