import sys
import math
n = int(input())
if n > 1 and n < 4:
if n == 2: print('1' + '\n' + '1')
else:
print('2' + '\n' + '1 3')
sys.exit()
print(n)
i = 2
while i<=n:
print(i, end = ' ' ); i+=2
i = 1
while i<=n:
print(i, end = ' '); i+=2
#include <iostream>
using namespace std;
int main()
{
long long n;
cin>>n;
if(n<=2)
{
cout<<1<<"\n"<<1;
}
else if(n==3)
{
cout<<2<<"\n"<<1<<" "<<3;
}
else if(n%2==0)
{
cout<<n<<"\n";
for(int i=n-1;i>=1;i--)
{
cout<<i<<" ";
i--;
}
for(int i=n;i>=2;i--)
{
cout<<i<<" ";
i--;
}
}
else
{
cout<<n<<"\n";
for(int i=n;i>=1;i--)
{
cout<<i<<" ";
i--;
}
for(int i=n-1;i>=2;i--)
{
cout<<i<<" ";
i--;
}
}
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