Happy sum#7807
It is known that a number is called happy if its decimal notation contains only the digits 4 and 7. For example, the numbers 4, 7, 47, 7777, and 4744474 are happy.
Let be the set of happy numbers such that a \le n \le b: S = \{ n :\; a \le n \le b,\; n is happy. Calculate the remainder when the following sum is divided by :
Two integers and (1 \le a \le b \le 10^{18}).
Output the remainder when the happy sum is divided by .
Example 1