input = STDIN.read.split("\n")

N = input[0].to_i
A = input[1]
B = input[2]
C = input[3]

cnt = 0

for i in 0..(N - 1)
    a = A[i]
    b = B[i]
    c = C[i]
    if a == b && b == c && a == c
        next
    end

    if a != b && b != c && a != c
        cnt = cnt + 2
        next
    end
    cnt = cnt + 1
end

puts cnt