B. Lucky Numberstime limit per test2 secondsmemory limit per test256 megabytesinputstandard inputoutputstandard outputPetya 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.InputThe only line contains a positive integer n (1 ≤ n ≤ 10100000). This number doesn't have leading zeroes.OutputOutput the least super lucky number that is more than or equal to n.ExamplesInput4500Output4747Input47Output47
Input4500
Output4747
['dp', 'greedy', '*1800']