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 C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<bits/stdc++.h>
using namespace std;
#define all(x) (x).begin(),(x).end()
long long int mod = 1e9+7;
int dx[4] = {0,1,0,-1};
int dy[4] = {1,0,-1,0};
//////////////////////////////////


int main(){
    int n; cin >> n;
    vector<int> a(n);
    for(int i=0; i<n; i++) cin >> a[i];
    vector<int> b = a;
    sort(all(b));
    int d = 0;
    for(int i=0; i<n; i++) {
        if(a[i] != b[i]) d++;
    }
    if(d == 2) cout << "YES" << endl;
    else cout << "NO" << endl;
    
    return 0;
}

// EOF