Imports System

Module Program
    Sub Main(args As String())
        Dim S As String = Console.ReadLine()
        Dim T As String = Console.ReadLine()

        Dim ans As Integer = 0
        For i As Integer = 1 To Len(S)
            If Mid(S, i, 1) <> Mid(T, i, 1) Then
                ans += 1
            End If
        Next

        Console.WriteLine(ans)

    End Sub
End Module
