n=gets.to_i
aString=gets.chomp.chars
bString=gets.chomp.chars
cString=gets.chomp.chars
sameCharCounts=[]
n.times do |index|
  stringCount = [aString[index],bString[index],cString[index]].count(aString[index])
  stringCount = 2 if stringCount == 1 && bString[index] == cString[index]
  sameCharCounts << stringCount
end
puts sameCharCounts.count(2) + sameCharCounts.count(1) * 2