Buggy python submission (verdict: Runtime Error):
while True:
   H, W = map(int, input().split())

   if H == 0 and W == 0:
      break

   for i in range(H/2):
      if H % 2 == 0:
         for j in range(W/2):
            if W % 2 == 0:
               print("#." * (W/2))
               print("")
               print(".#" * (W/2))
            else:
               print("#."*(W/2) + "#")
               print("")
               print(".#"*(W/2) + ".")
         print("")

      else:
         for j in range(W/2):
            if W % 2 == 0:
               print("#." * (W/2))
               print("")
               print(".#" * (W/2))
            else:
               print("#."*(W/2) + "#")
               print("")
               print(".#"*(W/2) + ".")
         if W % 2 == 0:
            print("#." * (W/2))
         else:
            print("#."*(W/2) + "#")
         print("")


Fixed submission:
while True:
   H, W = map(int, input().split())
   if H == 0 and W == 0:
      break
   for i in range(int(H/2)):
      if W % 2 == 0:
         print("#." * int(W/2))
      else:
         print("#."*int(W/2) + "#")
      if W % 2 == 0:
         print(".#" * int(W/2))
      else:
         print(".#"*int(W/2) + ".")
   if H % 2 != 0:
      if W % 2 == 0:
         print("#." * int(W/2))
      else:
         print("#."*int(W/2) + "#")
   print("")

Buggy python submission (verdict: Runtime Error):
while True:
   H, W = map(int, input().split())
   if H == 0 and W == 0:
      break
   for i in range(H/2):
      if W % 2 == 0:
         print("#." * (W/2))
      else:
         print("#."*(W/2) + "#")
      if W % 2 == 0
         print(".#" * (W/2))
      else:
         print(".#"*(W/2) + ".")
   if H % 2 != 0 
      if W % 2 == 0:
         print("#." * (W/2))
      else:
         print("#."*(W/2) + "#")
   print("")


Fixed submission:
while True:
   H, W = map(int, input().split())
   if H == 0 and W == 0:
      break
   for i in range(int(H/2)):
      if W % 2 == 0:
         print("#." * int(W/2))
      else:
         print("#."*int(W/2) + "#")
      if W % 2 == 0:
         print(".#" * int(W/2))
      else:
         print(".#"*int(W/2) + ".")
   if H % 2 != 0:
      if W % 2 == 0:
         print("#." * int(W/2))
      else:
         print("#."*int(W/2) + "#")
   print("")

Buggy python submission (verdict: Runtime Error):
while True:
   H, W = map(int, input().split())
   if H == 0 and W == 0:
      break
   for i in range(int(H/2)):
      if W % 2 == 0:
         print("#." * int(W/2))
      else:
         print("#."*int(W/2) + "#")
      if W % 2 == 0
         print(".#" * int(W/2))
      else:
         print(".#"*int(W/2) + ".")
   if H % 2 != 0 
      if W % 2 == 0:
         print("#." * int(W/2))
      else:
         print("#."*int(W/2) + "#")
   print("")


Fixed submission:
while True:
   H, W = map(int, input().split())
   if H == 0 and W == 0:
      break
   for i in range(int(H/2)):
      if W % 2 == 0:
         print("#." * int(W/2))
      else:
         print("#."*int(W/2) + "#")
      if W % 2 == 0:
         print(".#" * int(W/2))
      else:
         print(".#"*int(W/2) + ".")
   if H % 2 != 0:
      if W % 2 == 0:
         print("#." * int(W/2))
      else:
         print("#."*int(W/2) + "#")
   print("")