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>
#define REP(i, n) for(int i=0;i<int(n);++i)
using namespace std;
template<class A>void pr(A a){cout << a << endl;}
template<class A,class B>void pr(A a,B b){cout << a << " "  ;p(b);}
template<class A,class B,class C>void pr(A a,B b,C c){cout << a << " " ;p(b,c);}
template<class A,class B,class C,class D>void pr(A a,B b,C c,D d){cout << a << " " ;p(b,c,d);}
typedef long long ll;
typedef pair<ll, ll> l_l;
typedef pair<int, int> i_i;
int INF=numeric_limits<int>::max();
// for(int j=0;j<N;++j) {}

int main(void) {
  int n;cin>>n;
  int p[n+10];
  int q[n+10];
  REP(i,n) {
    int r;cin>>r;
    p[i]=r;
    q[i]=r;
  }

  // REP(i,n) pr(p[i]);

  sort(q,q+n);

  int cnt = 2;

  REP(i,n) {
    if(p[i]!=q[i]) {
      cnt-=1;
    }
  }
  if(cnt>=0) {
    pr("YES");
  } else {
    pr("NO");
  }
  return 0;
}