CF121A.Lucky Sum

普及/提高-

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题目描述

Petya loves lucky numbers. Everybody knows that lucky numbers are positive integers whose decimal representation contains only the lucky digits 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not.

Let $next(x)$ be the minimum lucky number which is larger than or equals $x$ . Petya is interested what is the value of the expression $next(l)+next(l+1)+...+next(r-1)+next(r)$ . Help him solve this problem.

输入格式

The single line contains two integers $l$ and $r$ ( $1<=l<=r<=10^{9}$ ) — the left and right interval limits.

输出格式

In the single line print the only number — the sum $next(l)+next(l+1)+...+next(r-1)+next(r)$ .

Please do not use the %lld specificator to read or write 64-bit integers in C++. It is preferred to use the cin, cout streams or the %I64d specificator.

输入输出样例

输入#1
```
2 7
```
输出#1
```
33
```
输入#2
```
7 7
```
输出#2
```
7
```

说明/提示

In the first sample: $next(2)+next(3)+next(4)+next(5)+next(6)+next(7)=4+4+4+7+7+7=33$

In the second sample: $next(7)=7$

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