【CodeForces 534A】Exam 【数学构造】

#include<bits/stdc++.h>
using namespace std;
int n;bool vis[5010];
int main(){
cin>>n;
if(n==1)cout<<1<<endl<<1;
else if(n==2)cout<<1<<endl<<1;
else if(n==3)cout<<2<<endl<<"1 3";
else
{
if(n%2==0){
cout<<n<<endl;
cout<<n/2+1<<" ";
for(int i=1;i<n/2;i++)
cout<<i<<" "<<n-i+1<<" ";
cout<<n/2;
}else
{
cout<<n<<endl;
cout<<n/2+1<<" ";
for(int i=1;i<=n/2;i++)
cout<<i<<" "<<n-i+1<<" ";
}
}
return 0;
}