构造

A. Exam time limit per test 1 second memory limit per test 256 megabytes input standard input output standard output An exam for n students will take place in a long and narrow room, so the students will sit in a line in some order. The teacher suspects that students with adjacent numbers (i and i + 1) always studied side by side and became friends and if they take an exam sitting next to each other, they will help each other for sure.

C - C **Time Limit:**1000MS **Memory Limit:**262144KB 64bit IO Format:%I64d & %I64u Submit Status Description Permutation_p_ is an ordered set of integers _p_1, p_2, …, p__n, consisting of n distinct positive integers not larger than n. We’ll denote as_n the length of permutation _p_1, _p_2, …, p__n.