import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int A = sc.nextInt();
		int B = sc.nextInt();
		sc.close();
		for(int i = 1; i <= 1009; i++) {
			int a = (int)(i * 0.08);
			int b = (int)(i * 0.10);
			if(a == A && b == 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