output_description: For each dataset, prints the number of prime numbers.
input_description: Input consists of several datasets. Each dataset has an integer n (1 ≤ n ≤
  999,999) in a line.
  
  The number of datasets is less than or equal to 30.
attempt: t = 0
  while t == 0:
      prime = [2, 3]
      try:
          n = int(input())
      except:
          break
      # ?¨??????\???????????????????¨????
      else:
          if n == 1:
              # 1?????????
              print(0)
          elif n == 2:
              print(1)
          elif n <= 4:
              print(2)
          else:
              a = 5
              while a > n:
                  # 5??\????????????
                  total = len(prime)
                  # ?´???°?????°?????????
                  for b in prime:
                      if a % b == 0:
                          break
                          # ?´???°??????????????´????????????
                      else:
                          if total == 0:
                              # ?´???°?¢?????????????
                              prime.append(a)
                          else:
                              # ?´???°??¢?´¢??°??????
                              total -= 1
                  if (a + 1) % 6 == 0:
                      a += 2
                  else:
                      a += 5
              print(len(prime))
  
problem_description: Prime Number
  
  Write a program which reads an integer n and prints the number of prime
  numbers which are less than or equal to n. A prime number is a natural number
  which has exactly two distinct natural number divisors: 1 and itself. For
  example, the first four prime numbers are: 2, 3, 5 and 7.
samples: [{"input": "3\n    11", "output": "2\n    5"}]