n = gets.to_i
a = gets.chomp.split("")
b = gets.chomp.split("")
c = gets.chomp.split("")
ans = 0
for i in 0..n-1 do
    s = [a[i],b[i],c[i]]
    if s.uniq.length == 2
        ans += 1
    elsif s.uniq.length == 3
        ans += 2
    end
end

puts ans