n = gets.chomp.to_i
a = gets.chomp.to_s
b = gets.chomp.to_s
c = gets.chomp.to_s
aa = []
bb = []
cc = []
a.each_byte { |x| aa << x }
b.each_byte { |x| bb << x }
c.each_byte { |x| cc << x }
result = 0
for m in 0..n - 1
  x = 0
  if aa[m] != bb[m]
    if bb[m] != cc[m]
      x = 2
    else
      x = 1
    end
  else
    if bb[m] != cc[m]
      x = 1
    else
      x = 0
    end
  end
  result = result + x
end
puts result
