Algorithm

A. Perfect Permutation
time limit per test
2 seconds
memory limit per test
256 megabytes
Problem link- https://codeforces.com/contest/233/problem/A
input
standard input
output
standard output

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 perfect permutation 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.

Examples
input
Copy
1
output
Copy
-1
input
Copy
2
output
Copy
2 1
input
Copy
4
output
Copy
2 1 4 3



 

Code Examples

#1 Code Example with C++ Programming

Code - C++ Programming

#include <bits/stdc++.h>

using namespace std;

int main() {
  int n;
  scanf("%d", &n);
  
  if(n & 1) {
    puts("-1");
    return 0;
  }
  
  for(int i = 0; i < n; i += 2)
    printf("%d %d ", i + 2, i + 1);
  puts("");
  
  return 0;
}
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Input

x
–
+
cmd
1

Output

x
–
+
cmd
-1
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Demonstration

Codeforcess Solution Perfect Permutation, A. Perfect Permutation ,C,C++, Java, Js and Python ,Perfect Permutation,Codeforcess Solution

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