President has declared the development of tram service a priority national project. As a part of this project, Yekaterinburg will receive enough budget funds to carry out a complete reconstruction of the city’s tram network.
There are 2ntram stops in Yekaterinburg. In the course of reconstruction, the stops will be left in their places and no new stops will be built, but new tram railways will be laid so that it will be possible to go by tram from every tram stop to any other tram stop without any intermediate stops.
Having studied messages at the tram forum, the city authorities found out that citizens would be satisfied with the reconstruction only if for every pair of tram stops there would be a tram route connecting these stops without any intermediate stops. It is clear that the network ofn(2n1) routes consisting of only two stops each satisfies this requirement. However, Yekaterinburg Mayor wants exactlynroutes to be left after the reconstruction, and each tram must make exactly 2nstops (including the final ones) on its route. Trams must go along these routes in both directions. Suggest a plan of reconstruction that will satisfy both citizens and Mayor.
Input
The only input line contains the integern,1 ≤n≤ 100.
Output
Outputnlines describing tram routes. Each route is a sequence of integers in the range from 1 to 2nseparated by a space. A route may go through a stop several times. If the problem has several solutions, you may output any of them. If there is no solution, output one line containing the number 1.
Sample
inputoutput
31 6 2 1 3 42 3 6 5 4 65 1 4 2 5 3
Problem Author:Alexander Ipatov (idea — Magaz Asanov)Problem Source:The 12th Urals Collegiate Programing Championship, March 29, 2008
，没有什么可留恋，只有抑制不住的梦想，
