Problem:
Score : 200 points

Problem Statement

We have a sequence p = {p_1,\ p_2,\ ...,\ p_N} which is a permutation of {1,\ 2,\ ...,\ N}.

You can perform the following operation at most once: choose integers i and j (1 \leq i < j \leq N), and swap p_i and p_j. Note that you can also choose not to perform it.

Print YES if you can sort p in ascending order in this way, and NO otherwise.

Constraints

All values in input are integers.

2 \leq N \leq 50

p is a permutation of {1,\ 2,\ ...,\ N}.

Input

Input is given from Standard Input in the following format:

N
p_1 p_2 ... p_N

Output

Print YES if you can sort p in ascending order in the way stated in the problem statement, and NO otherwise.

Sample Input 1

5
5 2 3 4 1

Sample Output 1

YES

You can sort p in ascending order by swapping p_1 and p_5.

Sample Input 2

5
2 4 3 5 1

Sample Output 2

NO

In this case, swapping any two elements does not sort p in ascending order.

Sample Input 3

7
1 2 3 4 5 6 7

Sample Output 3

YES

p is already sorted in ascending order, so no operation is needed.

Solution in Rust (1.15.1) (judge verdict: Accepted)

use std::io::prelude::*;

fn main() {
    let mut input_str = String::new();
    std::io::stdin().read_to_string(&mut input_str).unwrap();

    let input_parts = input_str.split_whitespace().collect::<Vec<_>>();
    let mut input_parts_it = input_parts.iter().cloned();

    let n: usize = input_parts_it.next().unwrap().parse().unwrap();

    let p: Vec<usize> = (0..n)
        .map(|_| input_parts_it.next().unwrap().parse().unwrap())
        .collect();
    let mut p2 = p.clone();

    let is_sorted = p.windows(2).all(|w| w[0] < w[1]);
    if is_sorted {
        println!("YES");
        return;
    }

    for k1 in 0..n {
        for k2 in k1..n {
            p2.clear();
            p2.extend(p.iter().cloned());
            p2.swap(k1, k2);

            let is_sorted = p2.windows(2).all(|w| w[0] < w[1]);
            if is_sorted {
                println!("YES");
                return;
            }
        }
    }

    println!("NO");
}