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--;
}
}
}1498A - GCD Sum | 1277C - As Simple as One and Two |
1301A - Three Strings | 460A - Vasya and Socks |
1624C - Division by Two and Permutation | 1288A - Deadline |
1617A - Forbidden Subsequence | 914A - Perfect Squares |
873D - Merge Sort | 1251A - Broken Keyboard |
463B - Caisa and Pylons | 584A - Olesya and Rodion |
799A - Carrot Cakes | 1569B - Chess Tournament |
1047B - Cover Points | 1381B - Unmerge |
1256A - Payment Without Change | 908B - New Year and Buggy Bot |
979A - Pizza Pizza Pizza | 731A - Night at the Museum |
742A - Arpa’s hard exam and Mehrdad’s naive cheat | 1492A - Three swimmers |
1360E - Polygon | 1517D - Explorer Space |
1230B - Ania and Minimizing | 1201A - Important Exam |
676A - Nicholas and Permutation | 431A - Black Square |
474B - Worms | 987B - High School Become Human |