Problem Statement  
The digits 4 and 7 are lucky digits, and all other digits are unlucky. A first level lucky number is a positive integer whose decimal representation is a palindrome that contains only lucky digits. A palindrome is a number that reads the same forward and backward. John and Brus would like to count the number of first level lucky numbers within a specified range. You are given longs a and b. Return the number of first level lucky numbers between a and b, inclusive.  
Definition  
 
Constraints  
  a will be between 1 and 10^18, inclusive.  
  b will be between a and 10^18, inclusive.  
Examples  
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