Option Explicit On
Option Strict On

Module Module1

    Sub Main()

        Dim N As Integer = CInt(Console.ReadLine())
        Dim A As String() = Split(Console.ReadLine(), " ")

        Array.Sort(A)

        Dim w As String = A(0)
        For i As Integer = 1 To A.Length - 1
            If w = A(i) Then
                Console.WriteLine("NO")
                End
            End If
            w = A(i)
        Next
        Console.WriteLine("YES")

    End Sub

End Module

