Codeforces 233A Perfect Permutation

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#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cstdio>
#include <math.h>
#include <string>
#include <algorithm>
#include <vector>

using namespace std;

int n;

int main() {
	scanf("%d", &n);
	if (n % 2 == 1) {
		printf("-1\n");
	}
	else {
		int l = n / 2;
		for (int i = 1;i <= l;++i) {
			printf("%d %d ", 2 * i, 2 * i - 1);
		}
	}
	return 0;
}