2111: Optimal Number Permutation
Time Limit: 2 Sec Memory Limit: 256 MBSubmit: 0 Solved: 0
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Description
time limit per test
1 secondmemory limit per test
256 megabytesinput
standard inputoutput
standard outputYou 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