CF686B Little Robber Girl's Zoo

Little Robber Girl likes to scare animals in her zoo for fun. She decided to arrange the animals in a row in the order of non-decreasing height. However, the animals were so scared that they couldn't stay in the right places. The robber girl was angry at first, but then she decided to arrange the animals herself. She repeatedly names numbers $ l $ and $ r $ such that $ r-l+1 $ is even. After that animals that occupy positions between $ l $ and $ r $ inclusively are rearranged as follows: the animal at position $ l $ swaps places with the animal at position $ l+1 $ , the animal $ l+2 $ swaps with the animal $ l+3 $ , ..., finally, the animal at position $ r-1 $ swaps with the animal $ r $ . Help the robber girl to arrange the animals in the order of non-decreasing height. You should name at most $ 20000 $ segments, since otherwise the robber girl will become bored and will start scaring the animals again.

The first line contains a single integer $ n $ ( $ 1

Print the sequence of operations that will rearrange the animals by non-decreasing height. The output should contain several lines, $ i $ -th of the lines should contain two space-separated integers $ l_{i} $ and $ r_{i} $ ( $ 1

Note that you don't have to minimize the number of operations. Any solution that performs at most $ 20000 $ operations is allowed.