#P95B. Lucky Numbers
Lucky Numbers
No submission language available for this problem.
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.
The only line contains a positive integer n (1 ≤ n ≤ 10100000). This number doesn't have leading zeroes.
Output the least super lucky number that is more than or equal to n.
Input
The only line contains a positive integer n (1 ≤ n ≤ 10100000). This number doesn't have leading zeroes.
Output
Output the least super lucky number that is more than or equal to n.
Samples
4500
4747
47
47