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 = []
  x << aa[m]
  x << bb[m]
  x << cc[m]
  x.uniq!
  result = result + x.length - 1
end
puts result
