n = gets.to_i
a,b,c = 3.times.map{gets.chomp}
ans = 0
for i in 0..n-1
    if a[i] == b[i] && b[i] == c[i]
        ans += 0
    elsif a[i] == b[i] || b[i] == c[i] || c[i] == a[i]
        ans += 1
    else
        ans += 2
    end
end
puts ans