Imports System

Module Program
    Sub Main(args As String())

        Dim sInputS As String = Console.ReadLine()
        Dim sInputT As String = Console.ReadLine()

        Dim iCount As Integer = 0

        For i = 0 To sInputS.Length - 1
            If sInputT(i) <> sInputS(i) Then
                iCount += 1
            End If
        Next i

        Console.WriteLine(iCount)

    End Sub
End Module
