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 Rust (1.15.1) (judge verdict: Accepted)

use std::io;
use std::collections::VecDeque;

fn main() {
    let mut input = Input::new();
    let n: i64 = input.next();
    let mut x: i64 = 0;
    let mut t: i64 = 0;
    let mut stack: VecDeque<(i64, i64)> = VecDeque::new();
    stack.push_back((-1, -1));
    for i in 0..n {
        let a: i64 = input.next();
        let mut j = i;
        loop {
            let (v, p) = *stack.back().unwrap();
            if v < a {
                t += (i - j + 1) * a;
                stack.push_back((a, j));
                break;
            }
            t -= (j - p) * v;
            j = p;
            stack.pop_back();
        }
        x += t;
    }
    println!("{}", x);
}

struct Input {
    queue: VecDeque<String>,
}

impl Input {
    fn new() -> Input {
        Input { queue: VecDeque::new() }
    }

    fn next<T>(&mut self) -> T
        where T: std::str::FromStr,
              T::Err: std::fmt::Debug
    {
        if self.queue.is_empty() {
            let mut line = String::new();
            let _ = io::stdin().read_line(&mut line);
            for x in line.split_whitespace() {
                self.queue.push_back(String::from(x));
            }
        }
        return self.queue.pop_front().unwrap().parse::<T>().unwrap();
    }
}