Buggy python submission (verdict: Time Limit Exceeded):
import sys

#+++++

		
def main():
	h , w = map(int, input().split())
	mm=[input() for _ in range(h)]
	
	rr_lr=[[0]*(w) for _ in range(h)]
	rr_rl=[[0]*(w) for _ in range(h)]
	rr_ud=[[0]*(w) for _ in range(h)]
	rr_du=[[0]*(w) for _ in range(h)]
							
	for hi in range(h):
		ll=0
		rl=0
		for wj in range(w):
			if mm[hi][wj] == '.':
				ll+=1
				rr_lr[hi][wj]=ll
			else:
				ll=0				
				
			if mm[hi][w-1-wj] == '.':
				rl+=1
				rr_rl[hi][w-1-wj]=rl
			else:
				rl=0				
					
	for wi in range(w):
		ll=0
		rl=0
		for hj in range(h):
			if mm[hj][wi] == '.':
				ll+=1
				rr_ud[hj][wi]=ll
			else:
				ll=0
				
			if mm[(h-1)-hj][wi] == '.':
				rl+=1
				rr_du[(h-1)-hj][wi]=rl
			else:
				rl=0
				
	ret=0
	for i in range(w):
		for j in range(h):
			vv=rr_lr[j][i]-3
			vv+=rr_rl[j][i]
			vv+=rr_du[j][i]
			vv+=rr_ud[j][i]
			ret = max(ret,vv)
	
	return ret

	
#+++++

if __name__ == "__main__":
	if sys.platform =='ios':
		sys.stdin=open('inputFile.txt')
		isTest=True
	else:
		pass
		input = sys.stdin.readline
			
	ret = main()
	if ret is not None:
		print(ret)

Fixed submission:
import sys

#+++++

		
def main():
	h , w = map(int, input().split())
	mm=[input() for _ in range(h)]
	
	rr_lr=[[0]*(w) for _ in range(h)]
	rr_rl=[[0]*(w) for _ in range(h)]
	rr_ud=[[0]*(w) for _ in range(h)]
	rr_du=[[0]*(w) for _ in range(h)]
							
	for hi in range(h):
		ll=0
		rl=0
		for wj in range(w):
			if mm[hi][wj] == '.':
				ll+=1
				rr_lr[hi][wj]=ll
			else:
				ll=0				
				
			if mm[hi][w-1-wj] == '.':
				rl+=1
				rr_rl[hi][w-1-wj]=rl
			else:
				rl=0				
					
	for wi in range(w):
		ll=0
		rl=0
		for hj in range(h):
			if mm[hj][wi] == '.':
				ll+=1
				rr_ud[hj][wi]=ll
			else:
				ll=0
				
			if mm[(h-1)-hj][wi] == '.':
				rl+=1
				rr_du[(h-1)-hj][wi]=rl
			else:
				rl=0
				
	ret=0
	for i in range(w):
		for j in range(h):
			vv=rr_lr[j][i]-3
			vv+=rr_rl[j][i]
			vv+=rr_du[j][i]
			vv+=rr_ud[j][i]
			ret = max(ret,vv)
	
	return ret

	
#+++++

if __name__ == "__main__":
	if sys.platform =='ios':
		sys.stdin=open('inputFile.txt')
		isTest=True
	else:
		pass
		input = sys.stdin.readline
			
	ret = main()
	if ret is not None:
		print(ret)

Buggy python submission (verdict: Time Limit Exceeded):
import sys

#+++++

		
def main():
	h , w = map(int, input().split())
	mm=[input() for _ in range(h)]
	
	rr_lr=[[0]*(w) for _ in range(h)]
	rr_rl=[[0]*(w) for _ in range(h)]
	rr_ud=[[0]*(w) for _ in range(h)]
	rr_du=[[0]*(w) for _ in range(h)]
							
	for hi in range(h):
		ll=0
		for wj in range(w):
			if mm[hi][wj] == '.':
				ll+=1
				rr_lr[hi][wj]=ll
			else:
				ll=0				
				
	for hi in range(h):
		ll=0
		for wj in range(w):
			if mm[hi][w-1-wj] == '.':
				ll+=1
				rr_rl[hi][w-1-wj]=ll
			else:
				ll=0				
					
	for wi in range(w):
		ll=0
		for hj in range(h):
			if mm[hj][wi] == '.':
				ll+=1
				rr_ud[hj][wi]=ll
			else:
				ll=0
				
	for wi in range(w):
		ll=0
		for hj in range(h):
			if mm[(h-1)-hj][wi] == '.':
				ll+=1
				rr_du[(h-1)-hj][wi]=ll
			else:
				ll=0
				
	ret=0
	for i in range(w):
		for j in range(h):
			vv=rr_lr[j][i]-3
			vv+=rr_rl[j][i]
			vv+=rr_du[j][i]
			vv+=rr_ud[j][i]
			ret = max(ret,vv)
	
	return ret

	
#+++++

if __name__ == "__main__":
	if sys.platform =='ios':
		sys.stdin=open('inputFile.txt')
		isTest=True
	else:
		pass
		input = sys.stdin.readline
			
	ret = main()
	if ret is not None:
		print(ret)

Fixed submission:
import sys

#+++++

		
def main():
	h , w = map(int, input().split())
	mm=[input() for _ in range(h)]
	
	rr_lr=[[0]*(w) for _ in range(h)]
	rr_rl=[[0]*(w) for _ in range(h)]
	rr_ud=[[0]*(w) for _ in range(h)]
	rr_du=[[0]*(w) for _ in range(h)]
							
	for hi in range(h):
		ll=0
		rl=0
		for wj in range(w):
			if mm[hi][wj] == '.':
				ll+=1
				rr_lr[hi][wj]=ll
			else:
				ll=0				
				
			if mm[hi][w-1-wj] == '.':
				rl+=1
				rr_rl[hi][w-1-wj]=rl
			else:
				rl=0				
					
	for wi in range(w):
		ll=0
		rl=0
		for hj in range(h):
			if mm[hj][wi] == '.':
				ll+=1
				rr_ud[hj][wi]=ll
			else:
				ll=0
				
			if mm[(h-1)-hj][wi] == '.':
				rl+=1
				rr_du[(h-1)-hj][wi]=rl
			else:
				rl=0
				
	ret=0
	for i in range(w):
		for j in range(h):
			vv=rr_lr[j][i]-3
			vv+=rr_rl[j][i]
			vv+=rr_du[j][i]
			vv+=rr_ud[j][i]
			ret = max(ret,vv)
	
	return ret

	
#+++++

if __name__ == "__main__":
	if sys.platform =='ios':
		sys.stdin=open('inputFile.txt')
		isTest=True
	else:
		pass
		input = sys.stdin.readline
			
	ret = main()
	if ret is not None:
		print(ret)

Buggy python submission (verdict: Time Limit Exceeded):
import sys

#+++++

def pp_in():
	s=input()
	return '#'+s+'#'
		
def main():
	h , w = map(int, input().split())
	mm=[pp_in() for _ in range(h)]
	ap='#'*(w+2)
	mm=[ap]+mm
	mm.append(ap)
	
	rr=[[[0,0] for _ in range(w+2)] for __ in range(h+2)]
	
	if isTest:
		for r in rr:
			print(r)
		for m in mm:
			print(m)
	
	for hi, hm in enumerate(mm):
		start=-1
		for wj, wc in enumerate(hm):
			if wc == '.' and start == -1:
				#it's new '.' pos.
				start=wj
			elif wc == '.':
				pass
			elif wc == '#' and start == -1:
				pass
			else:
				lb = wj - start
				for ii in range(start, wj):
					rr[hi][ii][0] = lb
				start=-1
	
	for wi in range(w+2):
		start=-1
		for hj in range(h+2):
			cc=mm[hj][wi]
			if cc == '.' and start == -1:
				#it's new '.' pos.
				start=hj
			elif cc == '.':
				pass
			elif cc == '#' and start == -1:
				pass
			else:
				lb = hj - start
				for ii in range(start, hj):
					rr[ii][wi][1] = lb
				start=-1
	
	if isTest:
		for r in rr:
			print(r)
			
	p_ret=max([max([sum(vv) for vv in r]) for r in rr])
	ret=p_ret-1
	return ret

	
#+++++
isTest=False

def pa(v):
	if isTest:
		print(v)

if __name__ == "__main__":
	if sys.platform =='ios':
		sys.stdin=open('inputFile.txt')
		isTest=True
	else:
		pass
		#input = sys.stdin.readline
			
	ret = main()
	if ret is not None:
		print(ret)

Fixed submission:
import sys

#+++++

		
def main():
	h , w = map(int, input().split())
	mm=[input() for _ in range(h)]
	
	rr_lr=[[0]*(w) for _ in range(h)]
	rr_rl=[[0]*(w) for _ in range(h)]
	rr_ud=[[0]*(w) for _ in range(h)]
	rr_du=[[0]*(w) for _ in range(h)]
							
	for hi in range(h):
		ll=0
		rl=0
		for wj in range(w):
			if mm[hi][wj] == '.':
				ll+=1
				rr_lr[hi][wj]=ll
			else:
				ll=0				
				
			if mm[hi][w-1-wj] == '.':
				rl+=1
				rr_rl[hi][w-1-wj]=rl
			else:
				rl=0				
					
	for wi in range(w):
		ll=0
		rl=0
		for hj in range(h):
			if mm[hj][wi] == '.':
				ll+=1
				rr_ud[hj][wi]=ll
			else:
				ll=0
				
			if mm[(h-1)-hj][wi] == '.':
				rl+=1
				rr_du[(h-1)-hj][wi]=rl
			else:
				rl=0
				
	ret=0
	for i in range(w):
		for j in range(h):
			vv=rr_lr[j][i]-3
			vv+=rr_rl[j][i]
			vv+=rr_du[j][i]
			vv+=rr_ud[j][i]
			ret = max(ret,vv)
	
	return ret

	
#+++++

if __name__ == "__main__":
	if sys.platform =='ios':
		sys.stdin=open('inputFile.txt')
		isTest=True
	else:
		pass
		input = sys.stdin.readline
			
	ret = main()
	if ret is not None:
		print(ret)