CodeforcesRound#144(Div.2)-A.PerfectPermutation_html/css

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A permutation is a sequence of integers p1,?p2,?...,?pn, consisting of n distinct positive integers, each of them doesn't exceed n. Let's denote the i-th element of permutation p as pi. We'll call number n the size of permutation p1,?p2,?...,?pn.

Nickolas adores permutations. He likes some permutations more than the others. He calls such permutations perfect. A perfectpermutation is such permutation p that for any i (1?≤?i?≤?n) (n is the permutation size) the following equations hold ppi?=?i and pi?≠?i. Nickolas asks you to print any perfect permutation of size n for the given n.

Input

A single line contains a single integer n (1?≤?n?≤?100) ? the permutation size.

Output

If a perfect permutation of size n doesn't exist, print a single integer -1. Otherwise print n distinct integers from 1 to n, p1,?p2,?...,?pn ? permutation p, that is perfect. Separate printed numbers by whitespaces.

Sample test(s)

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-1

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2 1 

input

output

2 1 4 3 

解题思路：贪心。直接构造。如果n为奇数，则不能构成满足要求的排列；否则，两个两个的构造，如2,1；4,3。。以此类推即可。

AC代码：

#include #include #include #include #include #include #include #include 

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