Option Infer On
Imports System.Collections.Generic
Imports System.Console

Module Program
    Sub Main()
        Dim dic = New Dictionary(Of Char, Boolean)
        Dim S As String = NextString()
        Dim ans = "yes"

        For Each v In S
            If dic.ContainsKey(v) Then
                ans = "no"
            End If
            dic(v) = True
        Next

        WriteLine(ans)
    End Sub

    Function NextString() As String
        Dim result As New List(Of Char)
        Do
            Dim tmp = Read()
            If tmp < 0 Then Exit Do
            Dim nextChar = Chr(tmp)

            If Not Char.IsWhiteSpace(nextChar) Then
                result.Add(nextChar)
            ElseIf nextChar <> vbCr Then
                Exit Do
            End If
        Loop
        Return New String(result.ToArray())
    End Function

End Module
