Public Class Main  
  Public Shared Sub Main(ByVal args() As String)
        
    Dim tmp() As String
    Dim N As Integer = Console.ReadLine()
'    Console.writeLine(N)

    tmp = split(Console.ReadLine())
    Dim i,j As Integer
    Dim A(N) As Integer
    For i = 0 To N-1
	    A(i) = tmp(i)
'    Console.writeLine(A(i))
  	Next i
  
  Dim ans As Boolean = True
  Dim num As Integer = 0
  Array.Sort(A)
  For i = 0 to N-2
  IF A(i)=A(i+1)
    Console.writeLine("NO")
    ans = False
    Exit For
  End If
Next i

If ans Then
Console.writeLine("YES")
Else
  ' Console.writeLine("NO")
End If
  
  End Sub
End Class
