Lucky Long

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Chef 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. Chef has a positive integer N. He can apply any of the following operations as many times as he want in any order: - Add 1 to the number N. - Take some digit of N and replace it b

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solution.cppC++17

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