lengthOfStrings = gets.to_i - 1
firstStrings  = gets.to_s
secondStrings = gets.to_s
thirdStrings  = gets.to_s

timesOfExchange = 0

for index in 0..lengthOfStrings do
    letterOfEachStrings = []
    letterOfEachStrings << firstStrings[index]
    letterOfEachStrings << secondStrings[index]
    letterOfEachStrings << thirdStrings[index]


    letterOfEachStrings =  letterOfEachStrings.uniq

    if letterOfEachStrings.size == 3 then
        timesOfExchange = timesOfExchange + 2
    elsif letterOfEachStrings.size == 2 then
        timesOfExchange = timesOfExchange + 1
    elsif letterOfEachStrings.size == 1 then
        timesOfExchange = timesOfExchange
    end
end

puts timesOfExchange