PROBLEM STATEMENT

John thinks 4 and 7 are lucky digits, and all other digits are not lucky.  A lucky number is a 
number that contains only lucky digits in decimal notation.



You are given ints a and b.  Return the number of lucky numbers between a and b, inclusive.



DEFINITION
Class:TheLuckyNumbers
Method:count
Parameters:int, int
Returns:int
Method signature:int count(int a, int b)


CONSTRAINTS
-a will be between 1 and 1,000,000,000, inclusive.
-b will be between a and 1,000,000,000, inclusive.


EXAMPLES

0)
1
10

Returns: 2

There are only two lucky numbers among the first ten positive integers.

1)
11
20

Returns: 0

But there are none among the next ten.

2)
74
77

Returns: 2

These two numbers are lucky. There are no additional lucky numbers between them.


3)
1000000
5000000

Returns: 64



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