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 5.4.1) (judge verdict: Accepted)

#include <iostream>
#include <cstdio>
using namespace std;

typedef long long LL;
const int N = 2e5 + 100;
struct Stack {
	int sep, idx;
};

Stack stk[N];
int n, top, a[N];
LL preSum, ans;

int main()
{
	scanf("%d", &n);
	for(int i = 1; i <= n; i ++) {
		scanf("%d", &a[i]);
	}
	for(int i = 1; i <= n; i ++ ) {
		int x = 0;
		while ( a[ stk[ top].idx] > a[i]) {
			x += stk[top].sep;
			preSum -= (LL)stk[top].sep * a[ stk[top].idx];
			top --;
		}
		stk[ ++ top].idx = i, stk[top].sep = x + 1;
		preSum += (LL)stk[top].sep * a[ stk[top].idx];
		ans += preSum;
	}
	printf("%lld\n", ans);
	return 0;
}