import java.util.*;
 
public class Main {
	public static void main(String[] args) {
    	Scanner sc = new Scanner(System.in);
		int n8 = sc.nextInt();
        int n10 = sc.nextInt();
        for(int i = 1; i <= 1000; i++){
        	if((int)(i * 0.08) == n8 && (int)(i * 0.1) == n10){
            	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