write a go solution for Description:
You are given an array a consisting of n integers. We denote the subarray a[l..r] as the array [a_l,a_l+1,...,a_r] (1<=l<=r<=n).

A subarray is considered good if every integer that occurs in this subarray occurs there exactly thrice. For example, the array [1,2,2,2,1,1,2,2,2] has three good subarrays:

- a[1..6]=[1,2,2,2,1,1];
- a[2..4]=[2,2,2];
- a[7..9]=[2,2,2].

Calculate the number of good subarrays of the given array a.

Input Format:
The first line contains one integer n (1<=n<=5*10^5).

The second line contains n integers a_1, a_2, ..., a_n (1<=a_i<=n).

Output Format:
Print one integer — the number of good subarrays of the array a.

Note:
None. Output only the code with no comments, explanation, or additional text.