import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int a = scanner.nextInt();
        int b = scanner.nextInt();
        int la,ra;
        if((a&1)==0){
            la = a*25/2;
            ra = (a+1)*25/2;
        }else{
            la = a*25/2 + 1;
            ra = (a+1)*25/2-1;
        }

        int lb = b*10;
        int rb = b*10+9;

        if(la>rb || ra<lb) System.out.println(-1);
        else System.out.println(Math.max(la,lb));
    }
}
/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