这题真的看不懂，求大佬指点

Question

_October has a question:
You are given n integers a1,a2,…,an. Find the maximum value of max(al,al+1,…,ar)⋅min(al,al+1,…,ar)over all pairs (l,r) of integers for which 1≤l<r≤n.

INPUT:

The first line contains a single integer n(2≤n≤10的3次方) .

The second line contains n integers a1,a2,…,an(1≤ai≤10的6次方).

OUTPUT:

Please print a single integer — the maximum possible value of the product from the statement.

SAMPLE INPUT1:

3
2 4 3

SAMPLE OUTPUT1:

12

Note:

Let f(l,r)=max(al,al+1,…,ar)⋅min(al,al+1,…,ar). In the first test case, f(1,2)=max(a1,a2)⋅min(a1,a2)=max(2,4)⋅min(2,4)=4⋅2=8. f(1,3)=max(a1,a2,a3)⋅min(a1,a2,a3)=max(2,4,3)⋅min(2,4,3)=4⋅2=8. f(2,3)=max(a2,a3)⋅min(a2,a3)=max(4,3)⋅min(4,3)=4⋅3=12. So the maximum is f(2,3)=12.

SAMPLE INPUT2:

4
3 2 3 1

SAMPLE OUTPUT2:

6

Advanced challenge ：What if the maxinum of n is 3∗10的5次方 ?

Answer 1

中文说就是输入一组数，函数f(l,r)的值是其中一个子区间[l,r]的最大值乘最小值，求最大的f(l,r)