codeforces 622D D. Optimal Number Permutation(找规律)

D. Optimal Number Permutation

time limit per test

1 second

memory limit per test

256 megabytes

input

standard input

output

standard output

You have array a that contains all integers from 1 to n twice. You can arbitrary permute any numbers in a.

Let number i be in positions xi, yi (xi < yi) in the permuted array a. Let's define the value di = yi - xi — the distance between the positions of the number i. Permute the numbers in array a to minimize the value of the sum .

Input

The only line contains integer n (1 ≤ n ≤ 5·105).

Output

Print 2n integers — the permuted array a that minimizes the value of the sum s.

Examples

input

2

output

1 1 2 2

input

1

output

1 1

题意：使给的上式的值最小，可以发现，最小值可以为0，把简单的几个列一下可以发现规律；

AC代码：

#include <bits/stdc++.h>
using namespace std;
int main()
{
    int n;
    scanf("%d",&n);
    if(n%2)
    {
        for(int i=1;i<=n;i+=2)
            printf("%d ",i);
        for(int i=n-2;i>0;i-=2)
            printf("%d ",i);
        for(int i=2;i<n;i+=2)
            printf("%d ",i);
        for(int i=n-1;i>0;i-=2)
            printf("%d ",i);
        printf("%d\n",n);
    }
    else
    {
        for(int i=1;i<=n;i+=2)
            printf("%d ",i);
        for(int i=n-1;i>0;i-=2)
            printf("%d ",i);
        for(int i=2;i<=n;i+=2)
            printf("%d ",i);
        for(int i=n-2;i>0;i-=2)
            printf("%d ",i);
        printf("%d\n",n);
    }
    return 0;
}