Longest Consecutive Subsequence

Given an array of integers, find the length of the longest subsequence in which every consecutive pair of numbers differs by exactly $1$. Note that the subsequence does not need to be contiguous in the original array. For example, in the array [1, 2, 3, 4, 6, 5, 7], the entire array forms a valid sequence and its length is 7.

inputFormat

The input is read from standard input. The first line contains an integer $n$, representing the number of elements in the array. The second line contains $n$ space-separated integers.

outputFormat

Print a single integer to standard output representing the length of the longest subsequence where the difference between every two consecutive elements is exactly $1$.## sample

7
1 2 3 4 6 5 7

7