300501: CF96B. Lucky Numbers (easy)

Memory Limit:256 MB Time Limit:2 S
Judge Style:Text Compare Creator:
Submit:0 Solved:0

Description

Lucky Numbers (easy)

题意翻译

super lucky number是只含有 $4$,$7$ 且 $4$ 的位数等于 $7$ 的位数的数字;寻找大于等于 $n(1\leq n\leq 10^9)$ 的最小super lucky number。

题目描述

Petya loves lucky numbers. Everybody knows that positive integers are lucky if their decimal representation doesn't contain digits other than $ 4 $ and $ 7 $ . For example, numbers $ 47 $ , $ 744 $ , $ 4 $ are lucky and $ 5 $ , $ 17 $ , $ 467 $ are not. Lucky number is super lucky if it's decimal representation contains equal amount of digits $ 4 $ and $ 7 $ . For example, numbers $ 47 $ , $ 7744 $ , $ 474477 $ are super lucky and $ 4 $ , $ 744 $ , $ 467 $ are not. One day Petya came across a positive integer $ n $ . Help him to find the least super lucky number which is not less than $ n $ .

输入输出格式

输入格式


The only line contains a positive integer $ n $ ( $ 1<=n<=10^{9} $ ). This number doesn't have leading zeroes.

输出格式


Output the least super lucky number that is more than or equal to $ n $ . 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

输入样例 #1

4500

输出样例 #1

4747

输入样例 #2

47

输出样例 #2

47

Input

题意翻译

super lucky number是只含有 $4$,$7$ 且 $4$ 的位数等于 $7$ 的位数的数字;寻找大于等于 $n(1\leq n\leq 10^9)$ 的最小super lucky number。

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