Permutation

给出整数$n,k$ 构造一个长度为$2n$的排列 $a$ 满足: $\sum_{i=1}^{n}\mid{a_{2i}-a_{2i-1}}\mid-\mid\sum_{i=1}^{n} a_{2i}-a_{2i-1} \mid=2*k$ 数据范围: $1≤n≤50000,0≤2k≤n$

A permutation $ p $ is an ordered group of numbers $ p_{1},p_{2},...,p_{n} $ , consisting of $ n $ distinct positive integers, each is no more than $ n $ . We'll define number $ n $ as the length of permutation $ p_{1},p_{2},...,p_{n} $ . Simon has a positive integer $ n $ and a non-negative integer $ k $ , such that $ 2k<=n $ . Help him find permutation $ a $ of length $ 2n $ , such that it meets this equation: .

The first line contains two integers $ n $ and $ k $ ( $ 1<=n<=50000 $ , $ 0<=2k<=n $ ).

Print $ 2n $ integers $ a_{1},a_{2},...,a_{2n} $ — the required permutation $ a $ . It is guaranteed that the solution exists. If there are multiple solutions, you can print any of them.

1 0

1 2

2 1

3 2 1 4

4 0

2 7 4 6 1 3 5 8

Record $ |x| $ represents the absolute value of number $ x $ . In the first sample $ |1-2|-|1-2|=0 $ . In the second sample $ |3-2|+|1-4|-|3-2+1-4|=1+3-2=2 $ . In the third sample $ |2-7|+|4-6|+|1-3|+|5-8|-|2-7+4-6+1-3+5-8|=12-12=0 $ .