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: Accepted)

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef vector<ll> vl;
typedef long double ld;
typedef vector<ld> vd;
typedef bool bl;
typedef vector<bl> vb;
typedef vector<vl> mt;
typedef unordered_map<ll,unordered_map<ll,ll>> graph;
typedef pair<ll,ll> pl;
typedef pair<ld,ld> pd;
typedef vector<string> vs;
typedef vector<vs> table;


const ll e5 = 1 << 20;
const ll mod = 1000000007;
const ll e3 = 1 << 13;
const ll INF = 1ll << 50;

const string pros = "YES";
const string cons = "NO";

ll n;
vl p;
ll cnt;

int main(){
  cin >> n;
  p = vl(n);
  for(ll i = 0;i < n;i++) cin >> p[i];
  for(ll i = 0;i < n;i++){
    if(p[i] != i+1) cnt++;
  }
  if(cnt == 2 || cnt == 0) cout << pros << endl;
  else cout << cons << endl;
}