Imports System

Module Program
    Sub Main(args As String())
        Dim LongN As Integer = Console.ReadLine()
        Dim tmpA As String() = Split(Console.ReadLine(), " ")
        Array.Sort(tmpA)
        Dim i As Integer = 0
        For i = 1 To LongN - 1
            If tmpA(i - 1) = tmpA(i) Then
                Console.WriteLine("NO")
                Exit Sub
            End If
        Next
        Console.WriteLine("YES")
    End Sub
End Module
