Lucky Unlucky

Chef believe in lucky and unlucky number. He thinks his 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. Unfortunately, not all numbers are lucky. He call a number nearly lucky if the number of lucky digits in it is a lucky number. He wonders whether number n is a nearl