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 (Clang 3.8.0) (judge verdict: Wrong Answer)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int array(int p[],int N);

int main(void){
  int N,p[55],r[55],i,j,c,k;
  char str[1000],*q;
  
  fgets(str,sizeof(str),stdin);
  N=atoi(str);
  fgets(str,sizeof(str),stdin);
  q=strtok(str," \n");
  p[0]=atoi(q);
  
  for(i=1;i<N;i++){
    q=strtok(NULL," \n");
  	p[i]=atoi(q);
  }
  
  if(array(p,N)==1){
    printf("Yes\n");
    return 0;
  }
  
  for(i=0;i<N-1;i++){
    for(j=i+1;j<N;j++){
      for(k=0;k<N;k++){
        r[k]=p[k];
      }
      c=r[i],r[i]=r[j],r[j]=c;
      if(array(r,N)==1){
        printf("Yes\n");
        return 0;
      }
    }
  }
  
  printf("No\n");
  
  return 0;
  
}

int array(int p[],int N){
  int i,j;
  
  for(i=0;i<N-1;i++){
    for(j=i+1;j<N;j++){
      if(p[i]>p[j]){
        return 0;
      }
    }
  }
  
  return 1;
  
}