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::{BufRead, Read};

pub struct Scanner<R>
where
    R: BufRead,
{
    reader: R,
}

impl<R> Scanner<R>
where
    R: BufRead,
{
    pub fn new(reader: R) -> Self {
        Scanner { reader: reader }
    }

    pub fn next<T>(&mut self) -> T
    where
        T: ::std::str::FromStr,
        <T as ::std::str::FromStr>::Err: ::std::fmt::Debug,
    {
        self.reader
            .by_ref()
            .bytes()
            .map(|b| b.unwrap() as char)
            .skip_while(|c| c.is_whitespace())
            .take_while(|c| !c.is_whitespace())
            .collect::<String>()
            .parse::<T>()
            .unwrap()
    }
}

fn main() {
    let stdin = std::io::stdin();
    let stdin = stdin.lock();
    let mut sc = Scanner::new(stdin);

    let n: usize = sc.next();
    let v: Vec<u8> = (0..n).map(|_| sc.next()).collect();
    let mut sv = v.clone();
    sv.sort();
    let mut count: i32 = 0;
    let mut answer: bool = true;
    for i in 0..n {
        if v[i] != sv[i] {
            count += 1;
            if count >= 3 {
                answer = false;
                break;
            }
        }
    }
    println!("{}", if answer { "YES" } else { "NO" });
}