# Lucky Numbers (easy)

Time Limit: 2 seconds

Memory Limit: 256 megabytes

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## Description

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.

## Input

The only line contains a positive integer n (1 ≤ n ≤ 109). This number doesn't have leading zeroes.

## Output

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.

## Sample Input

Input4500Output4747Input47Output47

## Sample Output

None

None

None