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.
|-||a will be between 1 and 10^18, inclusive.|
|-||b will be between a and 10^18, inclusive.|