def nikkei2019_b
    n = gets.chomp.to_i
    a = gets.chomp
    b = gets.chomp
    c = gets.chomp

    if a == b && b == c
        puts 0
        exit
    end

    cnt = 0
    for i in 0..n-1
        cnt += [a[i], b[i], c[i]].uniq.length - 1
    end

    puts cnt
end

nikkei2019_b