菜，就多练

#include <bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		if(i>n)
		{
			return 0;
		}
		if(i%2==0)
		{
			cout<<i-1<<" ";
		}
		if(i%2!=0)
		{
			cout<<i+1<<" ";
		}
	}
	
	return 0;
}