CF121C Lucky Permutation

Petya 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. One day Petya dreamt of a lexicographically $ k $ -th permutation of integers from $ 1 $ to $ n $ . Determine how many lucky numbers in the permutation are located on the positions whose indexes are also lucky numbers.

The first line contains two integers $ n $ and $ k $ $ (1

If the $ k $ -th permutation of numbers from $ 1 $ to $ n $ does not exist, print the single number "-1" (without the quotes). Otherwise, print the answer to the problem: the number of such indexes $ i $ , that $ i $ and $ a_{i} $ are both lucky numbers.

A permutation is an ordered set of $ n $ elements, where each integer from $ 1 $ to $ n $ occurs exactly once. The element of permutation in position with index $ i $ is denoted as $ a_{i} $ ( $ 1