import java.util.*;
import java.io.*; 

public class Main {
	
	public static void main(String... string) {
		Scanner sc = new Scanner(System.in);
		int x = sc.nextInt(); 
		int y = sc.nextInt();
		for(int i = 0; i<2000; i++) {
			if((int)(i*0.08) == x && (int)(i * 0.1) == y) {
				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