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()
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define repr(i, n) for(int i = n; i >= 0; i++)
#define REP(i, m, n) for(int i = m; i < n; i++)
#define SORT(v) sort((v).begin(), (v).end())
#define REV(v) sort((v).begin(), (v).end(), greater<int>())
#define INF 1000000007
typedef long long ll;
int gcd(int a,int b){return b?gcd(b,a%b):a;};
int lcm(int a,int b){return a * b / gcd(a, b);};
int month[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

int main() {
   int n;
   cin >> n;
   int p[n];
   int c = 0;
   rep(i, n) {
     cin >> p[i];
     if(p[i] != i + 1) c++;
   }
   if(c == 2) cout << "YES" << endl;
   else cout << "NO" << endl;
  return 0;
}