table = [true] * 500001
table[0] = table[1] = false

for i in 2..500000
  if table[i]
    for j in 2..500000/i
      table[i*j] = false
    end
  end
end

n = gets.to_i
(puts 0; exit) if n == 1

ans = 1
(2..n).select{|i| table[i]}.each do |r|
  p = 2
  q = r**2-p
  if 3 <= q && q <= n && table[q]
    ans += 2
  end
end

puts ans