TheYetAnotherLuckyNumbersProblem

Problem Statement

John and Brus believe that the digits 4 and 7 are lucky and all others are not. According to them, a lucky number is a number that contains only lucky digits in its decimal representation.

You are given longs A, B and C. Return the number of integers between A and B, inclusive, that can be represented as a sum of up to C lucky numbers.

Definition

Class:: TheYetAnotherLuckyNumbersProblem
Method:: find
Parameters:: long, long, long
Returns:: long
Method signature:: long find(long A, long B, long C)
(be sure your method is public)

Constraints

A will be between 1 and 474747474747474747, inclusive.
B will be between A and 474747474747474747, inclusive.
C will be between 1 and 7, inclusive.

Examples

```
1
```
```
12
```
```
2
```
```
Returns: 4
```
There are four numbers on this interval that are either lucky or can be represented as a sum of two lucky numbers: 4, 7, 8 = 4+4 and 11 = 4+7.
```
1
```
```
12
```
```
3
```
```
Returns: 5
```
The same numbers from the previous case and the nubmer 12 = 4+4+4.
```
4777778
```
```
7444443
```
```
1
```
```
Returns: 0
```
No lucky numbers on this interval.
```
1234567
```
```
9876543210
```
```
7
```
```
Returns: 6999664461
```

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