N = gets.to_i
A = gets.to_s.chars
B = gets.to_s.chars
C = gets.to_s.chars

df1 = (A - B).uniq.size
df2 = (B - C).uniq.size
df3 = (A - C).uniq.size
if df1 == 0 && df2 == 0 && df3 == 0
    p 0
else
    p df1 + df2 + df3
end