Option Explicit On
Option Strict On

Module Module1

    Sub Main()

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

        Dim A(N) As Integer
        For i As Integer = 0 To sA.Length - 1
            A(i) = Integer.Parse(sA(i))
        Next

        Array.Sort(A)

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

    End Sub

End Module
