write a go solution for Description:
Mr. Chanek gives you a sequence a indexed from 1 to n. Define f(a) as the number of indices where a_i=i.

You can pick an element from the current sequence and remove it, then concatenate the remaining elements together. For example, if you remove the 3-rd element from the sequence [4,2,3,1], the resulting sequence will be [4,2,1].

You want to remove some elements from a in order to maximize f(a), using zero or more operations. Find the largest possible f(a).

Input Format:
The first line contains one integer n (1<=n<=2*10^5) — the initial length of the sequence.

The second line contains n integers a_1,a_2,ldots,a_n (1<=qa_i<=q2*10^5) — the initial sequence a.

Output Format:
Output an integer denoting the largest f(a) that can be obtained by doing zero or more operations.

Note:
In the first example, f(A)=3 by doing the following operations.

[2,1,textbf4,2,5,3,7]arrow[textbf2,1,2,5,3,7]arrow[1,2,5,3,textbf7]arrow[1,2,textbf5,3]arrow[1,2,3]

In the second example, f(A)=2 and no additional operation is needed.. Output only the code with no comments, explanation, or additional text.