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::stdin;
use std::cmp::Ordering;

fn main() {
    let mut n = String::new();
    stdin().read_line(&mut n).unwrap();
    let n: usize = n.trim().parse().unwrap();

    let mut ps = String::new();
    stdin().read_line(&mut ps).unwrap();
    let mut ps: Vec<usize> = ps.trim().split_whitespace().flat_map(str::parse).collect();
    let mut sc = 0;
    for i in 0..n {
        if i + 1 < ps[i] {
            sc += 1;
        }
    }

    if sc > 1 {
        println!("NO");
    } else {
        println!("YES");
    }
}