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: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using static System.Console;
using static System.Math;

namespace C_ABC154
{
    class MainClass
    {

        static long[] n,s;

        public static void Main(string[] args)
        {

            n = Array.ConvertAll(ReadLine().Split().ToArray(), long.Parse);
            s = Array.ConvertAll(ReadLine().Split().ToArray(), long.Parse);

            var pf = s.ToList();
            var pfgrp = pf.GroupBy(a => a);
            if(pf.Count()==pfgrp.Count()){
                WriteLine("YES");
            }else{
                WriteLine("NO");
            }
        }
    }
}