import java.util.*;

class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int a = Integer.parseInt(sc.next());
		int b = Integer.parseInt(sc.next());
		
		int mini = 10000;
		
		for(int i = 1; i < 1001; ++i){
		    
		    int a_ans = (int)(i * 0.08);
		    int b_ans = (int)(i * 0.10);
		    
		    if((a_ans == a) && (b_ans == b)) {
		        if(mini >= i) mini = i;
		        else continue;
		    }
		    else continue;
		}
		
		//System.out.println(a);
		//System.out.println(b);
		//System.out.println(mini);
		
		if(mini == 10000) System.out.println(-1);
		else System.out.println(mini);
		
	}
}
/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