Imports System
Module Module1

    Sub Main()

        Dim n As Integer = Console.ReadLine
        Dim a As String = Console.ReadLine
        Dim b As String = Console.ReadLine
        Dim c As String = Console.ReadLine

        Dim cnt As Integer = 0

        Dim a1 As String
        Dim b1 As String
        Dim c1 As String
        For i As Integer = 1 To n
            a1 = Strings.Mid(a, i, 1)
            b1 = Strings.Mid(b, i, 1)
            c1 = Strings.Mid(c, i, 1)

            If a1 = b1 AndAlso b1 = c1 Then
            ElseIf a1 = b1 OrElse b1 = c1 OrElse c1 = a1 Then
                cnt += 1
            Else
                cnt += 2
            End If
        Next i

        Console.WriteLine(cnt)

    End Sub

End Module
