
Imports System.Console
Module Module1
    Sub Main()
        Dim s1 As String = ReadLine()
        Dim s2 As String = ReadLine()
        Dim c1() As Char = s1.ToCharArray
        Dim c2() As Char = s2.ToCharArray
        Dim ans As Integer
        For i = 0 To c1.Length - 1
            If c1(i) <> c2(i) Then
                ans += 1
            End If
        Next
        WriteLine(ans)
    End Sub
End Module
