require 'prime'
n = gets.to_i
if n == 1
  p 0
  exit 0
end

pli = Prime.take_while{|e| e <= n}.select{|q| 
  z = q+2
  h = Math.sqrt(z).to_i
  q != 2 && h**2 == z && h.prime?
}

p pli.size*2+1