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)

use std::io;

fn main() {
    let mut str = String::new();
    
    let mut _bytes_read = io::stdin().read_line(&mut str)
        .expect("Failed to read line");
//    let n: usize = str.trim().parse()
//        .expect("Failed to parse");
    
    let mut str2 = String::new();
    _bytes_read = io::stdin().read_line(&mut str2)
        .expect("Failed to read line");
    
    let parts: Vec<u32> = str2
        .trim()
        .split( ' ')
        .map(|s| s.parse().expect("Failed to parse"))
        .collect();
    
//    if n != parts.len() {
//        panic!("Invalid input");
//    }
    
//    println!("{}", n);
//    print_vec(parts)
    if can_swap(parts) {
        print!("YES");
    } else {
        print!("NO");
    }
}

//fn print_vec<T>(objs: Vec<T>) where T: std::fmt::Display {
//    for o in objs.iter() {
//        print!("{} ", o)
//    }
//    print!("\n");
//}

fn can_swap(objs: Vec<u32>) -> bool {
    let mut prev = objs[0];
    let mut mismatch = 0;
    for i in 1..(objs.len()) {
        let next = objs[i];
        if prev >= next {
            mismatch += 1;
            if mismatch > 2 {
                return false;
            }
        }
        prev = next;
    }
    
    return mismatch != 1;
}