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();

    int p = a*100 / 8;
    if (( a*100 % 8) !=0) {
      p = p+1;
    }
      //int q = b*10;
    int q = b*10;
    //出力
    if ( b == p/10 ) {
      System.out.println( p );
    } else if ( a == q*10/125) {
       System.out.println( q );
    }else{
      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