import java.util.*;
public class Main {
	public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        Random rand = new Random();
        
        int a = sc.nextInt();
        int b = sc.nextInt();
        int ans = -1;
        for(int i = 10000; i > 0; i--){
            int tax1 = (int)(i* 0.08);
            int tax2 = (int)(i* 0.1);
            if(tax1==a && tax2==b){
                ans = i;
            }
        }
        System.out.println(ans);

    
	}
}
/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