#include<bits/stdc++.h>
 using namespace std;

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
int n,k;
cin>>n;
if(n%2==0)
    k=n/2;

else
k=n/2+1;
cout<<k<<endl;
for(int i=1;i<=n;i++){
if(i<=k)
cout<<i<<" ";
}
     return 0;
 }