def factorial(number)
  #(1..number).inject(1,:*)
   number.step(1,-2).inject(1,:*)
end


N = gets.chomp.to_i(10)
temp = factorial(N).to_s.reverse
result = 0
  for i in 0..temp.length - 1
    if i != 0
      break
    end
    result = result + 1
  end
#puts factorial(N) % 998244353
puts result