len = gets.chomp.to_i
one = gets.chomp.split("")
two = gets.chomp.split("")
three = gets.chomp.split("")

array = []
len.times do |index|
    x = 0
    if one[index] != two[index]
        x += 1
    end
    if one[index] != three[index]
        x += 1
    end

    y = 0
    if two[index] != one[index]
        y += 1
    end
    if two[index] != three[index]
        y += 1
    end

    z = 0
    if three[index] != one[index]
        z += 1
    end
    if three[index] != two[index]
        z += 1
    end

    max = [x,y,z].min
    array.push(max)
end


print(array.reduce{|sum, n| sum+n})

