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();
		
		for(int i = 1; i <= 1250; i++) {
			if(Math.floor(i * 0.08) == A && Math.floor(i * 0.1) == B) {
				System.out.print(i);	
				sc.close();
				return;
			}
		}
		
		System.out.print(-1);		
		sc.close();
	}
	
}
/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