CF888D Almost Identity Permutations

A permutation $ p $ of size $ n $ is an array such that every integer from $ 1 $ to $ n $ occurs exactly once in this array. Let's call a permutation an almost identity permutation iff there exist at least $ n-k $ indices $ i $ ( $ 1

The first line contains two integers $ n $ and $ k $ ( $ 4

Print the number of almost identity permutations for given $ n $ and $ k $ .