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++ (GCC 9.2.1) (judge verdict: Accepted)

#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <cmath>
#include <stdio.h>
#include <queue>
#include <deque>
#include <cstdio>
#include <set>
#include <map>
#include <bitset>
#include <stack>
#include <cctype>
using namespace std;
vector<pair<long long, long long>> vec;
long long a;
int main() {
	long long n;
	cin >> n;
	for (long long i = 0; i < n; i++) {
		cin >> a;
		vec.emplace_back(make_pair(a, i + 1));
	}
	sort(vec.begin(), vec.end());
	set<long long> st;
	st.insert(0);
	st.insert(n + 1);
	long long ans = 0;
	for (int i = 0; i < n; i++) {
		long long x = vec[i].first;
		long long y = vec[i].second;
		auto itr = st.set::lower_bound(y);
		auto itr1 = itr--;
		ans += x * (y - *itr1) * (*itr - y);
		st.insert(y);
	}
	cout << ans << endl;
}