import java.util.*;

class Main {
    Scanner sc = new Scanner(System.in);

    public static void main(String[] args) {
        Main m = new Main();
        m.run();
    }

    private void run() {
        int a = sc.nextInt();
        int b = sc.nextInt();

        for (int i = 0; i < 1250; i++) {
            int p1 = (int) Math.floor(i * 0.08);
            int p2 = (int) Math.floor(i * 0.1);
            if (p1 == a && p2 == 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