import sys
import math
input = lambda: sys.stdin.readline().rstrip()

#  -----------------------  #

n = int(input())
if n % 2 == 0:
  print(n//2)
else:
  if n % 4 == 3:
    print(math.ceil(n/2)//2)
  else:
    print(math.ceil(n/2)//2 + 1)