N=gets.to_i
A=gets.chomp
B=gets.chomp
C=gets.chomp
c=0
for i in 0...N do
    if A[i]!=B[i] && B[i]!=C[i] && C[i]!=A[i] then
        c+=2
    elsif A[i]!=B[i] then
        c+=1
    elsif B[i]!=C[i] then
        c+=1
    elsif C[i]!=A[i] then
        c+=1
    end
end
p c