Problem:
Score : 400 points

Problem Statement

One day, Snuke was given a permutation of length N, a_1, a_2, ..., a_N, from his friend.

Find the following:

Constraints

1 ≦ N ≦ 200,000

(a_1, a_2, ..., a_N) is a permutation of (1, 2, ..., N).

Input

The input is given from Standard Input in the following format:

N
a_1 a_2 ... a_N

Output

Print the answer.

Note that the answer may not fit into a 32-bit integer.

Sample Input 1

3
2 1 3

Sample Output 1

9

Sample Input 2

4
1 3 2 4

Sample Output 2

19

Sample Input 3

8
5 4 8 1 2 6 7 3

Sample Output 3

85

Solution in C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <iostream>
#include <set>

using namespace std;

int main(){
	long  sum = 0;
	int n;
	int a[200001];
	int pos[20001];
	set<int> s;

	cin >> n;
	for (int i = 1; i <= n; i++)
	{
		cin >> a[i];
		pos[a[i]] = i;
	}

	s.insert(0);
	s.insert(n+1);


	for (int i = 1; i <= n; i++)
	{
		int l, r;
		// s.insert(pos[i]);
		set<int>::iterator itr = s.lower_bound(pos[i]);
		r = *(itr) - pos[i];
		// --itr;
		l = pos[i] - *(--itr);

		// if(itr == --s.end()){
		// 	r = n - *itr;
		// }else{
		// 	itr++;
		// 	r = *itr - *(--itr);
		// }
		// if(itr == s.begin()){
		// 	l = *itr + 1;
		// }else{
		// 	l = *itr - *(--itr);
		// } 
		s.insert(pos[i]);

		sum += (long)i * r * l;
	}
	cout << sum << endl;
	return 0;
}