n = gets.chomp.to_i
a = gets.chomp.split("")
b = gets.chomp.split("")
c = gets.chomp.split("")
total = 0

for i in 0..n
  if a[i] == b[i] && a[i] == c[i]
  elsif a[i] != b[i] && a[i] != c[i] && b[i] != c[i]
  total += 2
  else
  total += 1
  end
end

puts total