import java.util.Scanner;
public class Main {

	public static void main(String[] args) {
		Scanner stdIn = new Scanner(System.in);
		
		int a = stdIn.nextInt();
		int b = stdIn.nextInt();
		
		for(int i = 10; i < 1010; i++) {
			if((int)(i * 0.08) == a && (int)(i*0.1) == b) {
				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