Avin is studying series. A series is called "wave" if the following conditions are satisfied: 1) It contains at least two elements; 2) All elements at odd positions are the same; 3) All elements at even positions are the same; 4) Elements at odd positions are NOT the same as the elements at even positions. You are given a series with length n. Avin asks you to find the longest "wave" subseries. A subseries is a subsequence of a series.
输入解释
The first line contains two numbers n, c (1 ≤ n ≤ 100, 000, 1 ≤ c ≤ 100). The second line contains n integers whose range is [1, c], which represents the series. It is guaranteed that there is always a "wave" subseries.