CF109D Lucky Sorting

Petya loves lucky numbers. We all know that lucky numbers are the positive integers whose decimal representations contain only the lucky digits 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not. Petya got an array consisting of $ n $ numbers, it is the gift for his birthday. Now he wants to sort it in the non-decreasing order. However, a usual sorting is boring to perform, that's why Petya invented the following limitation: one can swap any two numbers but only if at least one of them is lucky. Your task is to sort the array according to the specified limitation. Find any possible sequence of the swaps (the number of operations in the sequence should not exceed $ 2n $ ).

The first line contains an integer $ n $ ( $ 1

On the first line print number $ k $ ( $ 0