n = gets.to_i
a = gets.chomp.split("")
b = gets.chomp.split("")
c = gets.chomp.split("")
ans = 0
for i in 0..n-1
  if a[i] != b[i] && b[i] != c[i] && c[i] != a[i]
    ans += 2
  elsif a[i] == b[i] && b[i] == c[i] && c[i] == a[i]
  else
    ans += 1
  end
end
puts ans
