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