n = gets.to_i
a = gets.to_s
b = gets.to_s
c = gets.to_s

cnt = 0
for i in 0..n-1 do
  if ((a[i]== b[i]) && (a[i] != c[i])) or
     ((a[i]== c[i]) && (a[i] != b[i])) or
     ((b[i]== c[i]) && (a[i] != b[i]))
    cnt += 1
  elsif (a[i]!=b[i]) && (a[i]!=c[i])
    cnt += 2
  end
end
puts cnt