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: Wrong Answer)



fn main() {
    let _n: usize = read();
    let p: Vec<i32> = read_vec();

    if carv(p) >= 3 {
        println!("NO");
    } else {
        println!("YES");
    }

}

fn carv(v: Vec<i32>) -> i32 {
    let mut ans = 0;
    for i in 0..v.len() - 2 {
        if (v[i] - v[i+1]) * (v[i+1] - v[i+2]) < 0 {
            ans += 1
        }
    }
    ans
}


//**********************************************************************************************************************************************//

// 標準入力から一行を読み取り、指定の型に変換する関数
pub fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

// 標準入力から一行を読み取り、空白文字で分割し、各要素を指定の型に変換する関数
pub fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}

// 標準入力からn行を読み取り、各行を空白文字で分割し、各要素を指定の型に変換する関数
pub fn read_vec2<T: std::str::FromStr>(n: u64) -> Vec<Vec<T>> {
    (0..n).map(|_| read_vec()).collect()
}

// 10進数での各桁の和
pub fn sum_dights(x: isize) -> isize {
    if x % 10 == 0 {
        return 0
    }
    let m = x % 10;
    m + sum_dights((x - m) / 10)
}