n = gets.to_i

s = Array.new(3)
s[0] = gets.chomp
s[1] = gets.chomp
s[2] = gets.chomp

ans = 0
for i in 0...n
    a = s[0][i]
    b = s[1][i]
    c = s[2][i]
    
    same = 0
    same += 1 if a == b
    same += 1 if b == c
    same += 1 if c == a

    if same == 0
        ans += 2
    elsif same == 1
        ans += 1
    else

    end
end

puts ans