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)

fn read_one<T : std::str::FromStr>() -> T {
    let mut input = String::new();
    std::io::stdin().read_line(&mut input).unwrap();
    input.trim().parse().ok().unwrap()
}

/// 1行の文字を空白で分割してVec<T>にする。
fn read_split<T : std::str::FromStr>() -> Vec<T> {
    let mut input = String::new();
    std::io::stdin().read_line(&mut input).unwrap();
    input.trim().split_whitespace().map(|x| x.parse().ok().unwrap()).collect()
}

fn main() {
    let input1 : usize = read_one();
    let input2 : Vec<i32> = read_split();
    let mut input2sorted = input2.clone();
    input2sorted.sort();
    let mut badcount = 0;
    for i in 0..input1 {
        if input2[i] != input2sorted[i] { badcount += 1; }
    }
    
    println!("{}", if badcount > 2 { "NO" } else { "YES" });
}