Problem:
Score : 300 points

Problem Statement

Given is a sequence of integers A_1, A_2, ..., A_N.
If its elements are pairwise distinct, print YES; otherwise, print NO.

Constraints

2 ≤ N ≤ 200000

1 ≤ A_i ≤ 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_1 ... A_N

Output

If the elements of the sequence are pairwise distinct, print YES; otherwise, print NO.

Sample Input 1

5
2 6 1 4 5

Sample Output 1

YES

The elements are pairwise distinct.

Sample Input 2

6
4 1 3 1 6 2

Sample Output 2

NO

The second and fourth elements are identical.

Sample Input 3

2
10000000 10000000

Sample Output 3

NO

Solution in C# (Mono 4.6.2.0) (judge verdict: Time Limit Exceeded)

using System;
using System.Collections.Generic;

class Program
{
  static void Main()
  {
    Console.ReadLine();
    List<int> a = new List<int>();
    string[] str = Console.ReadLine().Split();
    
    int n;
    
    foreach(string s in str)
      a.Add(int.Parse(s));
    
    while(a.Count > 0)
    {
      n = a.Count;
      
      a.RemoveAll(x => x == a[0]);
      
      if(n - a.Count > 1)
      {
        Console.WriteLine("NO");
        return;
      }
    }
    
    Console.WriteLine("YES");
  }
}