Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
H,W=map(int,input().split())
white=0
s=[]
for y in range(H):
    line=input()
    white+=line.count('.')
    s.append(list(line))

q = deque([(0,0,1)])
q_append=q.append
q_popleft=q.popleft
while q:
    x,y,l=q_popleft()
    if s[y][x]!='.':
        continue
    if x==W-1 and y==H-1:
        print(white-l)
        break
    for d in [(1,0),(0,1),(-1,0),(0,-1)]:
        nx, ny=(x+d[0],y+d[1])
        if 0<=nx<W and 0<=ny<H:
            q_append((nx,ny,l+1))
else:
    print(-1)

Fixed submission:
from collections import deque
H,W=map(int,input().split())
white=0
s=[]
for y in range(H):
    line=input()
    white+=line.count('.')
    s.append(list(line))

q = deque([(0,0,1)])
q_append=q.append
q_popleft=q.popleft
while q:
    x,y,l=q_popleft()
    if s[y][x]!='.':
        continue
    if x==W-1 and y==H-1:
        print(white-l)
        break
    s[y][x]='*'
    for d in [(1,0),(0,1),(-1,0),(0,-1)]:
        nx, ny=(x+d[0],y+d[1])
        if 0<=nx<W and 0<=ny<H:
            q_append((nx,ny,l+1))
else:
    print(-1)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
H,W=map(int,input().split())
white=0
s=[]
for y in range(H):
    line=input()
    white+=line.count('.')
    s.append(list(line))

q = deque([(0,0,1)])
q_append=q.append
q_popleft=q.popleft
while q:
    x,y,l=q_popleft()
    if s[y][x]!='.':
        continue
    if x==W-1 and y==H-1:
        print(white-l)
        break
    for d in [(1,0),(0,1),(-1,0),(0,-1)]:
        nx, ny=(x+d[0],y+d[1])
        if 0<=nx<W and 0<=ny<H:
            q_append((nx,ny,l+1))
else:
    print(-1)

Fixed submission:
from collections import deque
H,W=map(int,input().split())
white=0
s=[]
for y in range(H):
    line=input()
    white+=line.count('.')
    s.append(list(line))

q = deque([(0,0,1)])
q_append=q.append
q_popleft=q.popleft
while q:
    x,y,l=q_popleft()
    if s[y][x]!='.':
        continue
    if x==W-1 and y==H-1:
        print(white-l)
        break
    s[y][x]='*'
    for d in [(1,0),(0,1),(-1,0),(0,-1)]:
        nx, ny=(x+d[0],y+d[1])
        if 0<=nx<W and 0<=ny<H:
            q_append((nx,ny,l+1))
else:
    print(-1)

Buggy python submission (verdict: Runtime Error):
from collections import deque
H,W=map(int,input().split())
white=0
s=[]
for y in range(H):
   line=input()
    white+=line.count('.')
    s.append(list(line))
     
q = deque([(0,0,1)])
q_append=q.append
q_popleft=q.popleft
while q:
    x,y,l=q_popleft()
    if s[y][x]!='.':
        continue
    if x==W-1 and y==H-1:
        print(white-l)
        break
    s[y][x]='*'
    for d in [(1,0),(0,1),(-1,0),(0,-1)]:
        nx, ny=(x+d[0],y+d[1])
        if 0<=nx<W and 0<=ny<H:
            q_append((nx,ny,l+1))
else:
    print(-1)
        

Fixed submission:
from collections import deque
H,W=map(int,input().split())
white=0
s=[]
for y in range(H):
    line=input()
    white+=line.count('.')
    s.append(list(line))

q = deque([(0,0,1)])
q_append=q.append
q_popleft=q.popleft
while q:
    x,y,l=q_popleft()
    if s[y][x]!='.':
        continue
    if x==W-1 and y==H-1:
        print(white-l)
        break
    s[y][x]='*'
    for d in [(1,0),(0,1),(-1,0),(0,-1)]:
        nx, ny=(x+d[0],y+d[1])
        if 0<=nx<W and 0<=ny<H:
            q_append((nx,ny,l+1))
else:
    print(-1)

Buggy python submission (verdict: Runtime Error):
from collections import deque
H,W=map(int,input().split())
white=0
s=[]
for y in range(H):
   line=input()
    white+=line.count('.')
    s.append(list(line))
     
q = deque([(0,0,1)])
q_append=q.append
q_popleft=q.popleft
while q:
    x,y,l=q_popleft()
    if s[y][x]!='.':
        continue
    if x==W-1 and y==H-1:
        print(white-l)
        break
    s[y][x]='*'
    for d in [(1,0),(0,1),(-1,0),(0,-1)]:
        nx, ny=(x+d[0],y+d[1])
        if 0<=nx<W and 0<=ny<H:
            q_append((nx,ny,l+1))
else:
    print(-1)
        

Fixed submission:
from collections import deque
H,W=map(int,input().split())
white=0
s=[]
for y in range(H):
    line=input()
    white+=line.count('.')
    s.append(list(line))

q = deque([(0,0,1)])
q_append=q.append
q_popleft=q.popleft
while q:
    x,y,l=q_popleft()
    if s[y][x]!='.':
        continue
    if x==W-1 and y==H-1:
        print(white-l)
        break
    s[y][x]='*'
    for d in [(1,0),(0,1),(-1,0),(0,-1)]:
        nx, ny=(x+d[0],y+d[1])
        if 0<=nx<W and 0<=ny<H:
            q_append((nx,ny,l+1))
else:
    print(-1)

Buggy python submission (verdict: Runtime Error):
    from collections import deque
    H,W=map(int,input().split())
    white=0
    s=[]
    for y in range(H):
        line=input()
        white+=line.count('.')
        s.append(list(line))
     
    q = deque([(0,0,1)])
    q_append=q.append
    q_popleft=q.popleft
    while q:
        x,y,l=q_popleft()
        if s[y][x]!='.':
            continue
        if x==W-1 and y==H-1:
            print(white-l)
            break
        for d in [(1,0),(0,1),(-1,0),(0,-1)]:
            nx, ny=(x+d[0],y+d[1])
            if 0<=nx<W and 0<=ny<H:
                q_append((nx,ny,l+1))
    else:
        print(-1)
        

Fixed submission:
from collections import deque
H,W=map(int,input().split())
white=0
s=[]
for y in range(H):
    line=input()
    white+=line.count('.')
    s.append(list(line))

q = deque([(0,0,1)])
q_append=q.append
q_popleft=q.popleft
while q:
    x,y,l=q_popleft()
    if s[y][x]!='.':
        continue
    if x==W-1 and y==H-1:
        print(white-l)
        break
    s[y][x]='*'
    for d in [(1,0),(0,1),(-1,0),(0,-1)]:
        nx, ny=(x+d[0],y+d[1])
        if 0<=nx<W and 0<=ny<H:
            q_append((nx,ny,l+1))
else:
    print(-1)