Imports System

Imports System.Text.RegularExpressions

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Public Module Module1

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    Public Sub Main()

        If IsValid("Five hun5dred") Then

            Console.WriteLine("Valid")

        Else

            Console.WriteLine("InValid")

        End If

    End Sub

    Public Function IsValid(NoOfGuests As String) As Boolean

        Dim regex As Regex = New Regex("\d+")

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        If String.IsNullOrEmpty(NoOfGuests) Then

            Return True

        End If

        Return regex.IsMatch(NoOfGuests)

    End Function

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End Module

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