text: import sys
  
  if len(sys.argv) < 1:
      print("Input file expected", file=sys.stderr)
      sys.exit(1)
  
  
  with open(sys.argv[1]) as infile:
      x = 0
      trees = 0
      for slope in infile:
          slope = slope.strip()
          if slope[x % len(slope)] == '#':
                  trees += 1
          x += 3
  
      print(f"You hit {trees} trees")
  
      # To run py day03.py list.txt