#!/usr/local/bin/python2.7



   def main():

       total = 0;

       with open("day1.txt", 'r') as f:
          lines = f.readlines()

          for x in lines:
              values = int(x)
              new_values = ((values / 3) - 2)
              total += new_values
          print(total)


  if __name__ == "__main__":
      main()