Buggy python submission (verdict: Runtime Error):
H,W = map(int,input().split())
Grid = [[1 if g == "." else 0 for g in input()] for _ in range(H)]
dp = [[10**5]*(W) for _ in range(H)]
dp[0][0] = 0
black = 0
flag = Grid[0][0]

for g in Grid:
    for gg in g:
        if not(gg):
            black += 1

a = [-1,1]
def bfs(grid,h,w,Q):
    if h == H - 1 and w == W - 1:
        return dp[h][w]
    for aa in a:
        if 0 <= h + aa <= H -1:
            if grid[h+aa][w]:
                grid[h+aa][w] = 0
                dp[h+aa][w] = dp[h][w] + 1
                Q.append([h+aa,w])
        if 0 <= w + aa <= W - 1:
            if grid[h][w+aa]:
                grid[h][w+aa] = 0
                dp[h][w+aa] = dp[h][w] + 1
                Q.append([h,w + aa])
    if len(Q) == 0:
        return -1
    else:
        nexth,nextw = Q.pop(0)
        return bfs(grid,nexth,nextw,Q)
queue = []
Grid[0][0] = 0
if  flag:
    ans = bfs(Grid,0,0,queue)
    if ans == -1:
        print(-1)
    else:
        print(H*W - ans - 1 - black)
else:
    print(-1)


Fixed submission:
H,W = map(int,input().split())
Grid = [[1 if g == "." else 0 for g in input()] for _ in range(H)]
dp = [[10**5]*(W) for _ in range(H)]
dp[0][0] = 0
black = 0
flag = Grid[0][0]

for g in Grid:
    for gg in g:
        if not(gg):
            black += 1

a = [-1,1]

import sys
sys.setrecursionlimit(10**4)
def bfs(grid,h,w,Q):
    if h == H - 1 and w == W - 1:
        return dp[h][w]
    for aa in a:
        if 0 <= h + aa <= H -1:
            if grid[h+aa][w]:
                grid[h+aa][w] = 0
                dp[h+aa][w] = dp[h][w] + 1
                Q.append([h+aa,w])
        if 0 <= w + aa <= W - 1:
            if grid[h][w+aa]:
                grid[h][w+aa] = 0
                dp[h][w+aa] = dp[h][w] + 1
                Q.append([h,w + aa])
    if len(Q) == 0:
        return -1
    else:
        nexth,nextw = Q.pop(0)
        return bfs(grid,nexth,nextw,Q)
queue = []
Grid[0][0] = 0
if  flag:
    ans = bfs(Grid,0,0,queue)
    if ans == -1:
        print(-1)
    else:
        print(H*W - ans - 1 - black)
else:
    print(-1)

Buggy python submission (verdict: Runtime Error):
H,W = map(int,input().split())
Grid = [[1 if g == "." else 0 for g in input()] for _ in range(H)]
dp = [[10**5]*(W) for _ in range(H)]
dp[0][0] = 0
black = 0
flag = Grid[H-1][W-1]

for g in Grid:
    for gg in g:
        if not(gg):
            black += 1

a = [-1,1]
def bfs(grid,h,w,Q):
    if h == H - 1 and w == W - 1:
        return dp[h][w]
    for aa in a:
        if 0 <= h + aa <= H -1:
            if grid[h+aa][w]:
                grid[h+aa][w] = 0
                dp[h+aa][w] = dp[h][w] + 1
                Q.append([h+aa,w])
        if 0 <= w + aa <= W - 1:
            if grid[h][w+aa]:
                grid[h][w+aa] = 0
                dp[h][w+aa] = dp[h][w] + 1
                Q.append([h,w + aa])
    if len(Q) == 0:
        return -1
    else:
        nexth,nextw = Q.pop(0)
        return bfs(grid,nexth,nextw,Q)
queue = []
if Grid[0][0] and flag:
    ans = bfs(Grid,0,0,queue)
    if ans == -1:
        print(-1)
    else:
        print(H*W - ans - 1 - black)
else:
    print(-1)


Fixed submission:
H,W = map(int,input().split())
Grid = [[1 if g == "." else 0 for g in input()] for _ in range(H)]
dp = [[10**5]*(W) for _ in range(H)]
dp[0][0] = 0
black = 0
flag = Grid[0][0]

for g in Grid:
    for gg in g:
        if not(gg):
            black += 1

a = [-1,1]

import sys
sys.setrecursionlimit(10**4)
def bfs(grid,h,w,Q):
    if h == H - 1 and w == W - 1:
        return dp[h][w]
    for aa in a:
        if 0 <= h + aa <= H -1:
            if grid[h+aa][w]:
                grid[h+aa][w] = 0
                dp[h+aa][w] = dp[h][w] + 1
                Q.append([h+aa,w])
        if 0 <= w + aa <= W - 1:
            if grid[h][w+aa]:
                grid[h][w+aa] = 0
                dp[h][w+aa] = dp[h][w] + 1
                Q.append([h,w + aa])
    if len(Q) == 0:
        return -1
    else:
        nexth,nextw = Q.pop(0)
        return bfs(grid,nexth,nextw,Q)
queue = []
Grid[0][0] = 0
if  flag:
    ans = bfs(Grid,0,0,queue)
    if ans == -1:
        print(-1)
    else:
        print(H*W - ans - 1 - black)
else:
    print(-1)

Buggy python submission (verdict: Runtime Error):
H,W = map(int,input().split())
Grid = [[1 if g == "." else 0 for g in input()] for _ in range(H)]
dp = [[10**5]*(W) for _ in range(H)]
dp[0][0] = 0
black = 0

for g in Grid:
    for gg in g:
        if not(gg):
            black += 1

a = [-1,1]
def bfs(grid,h,w,Q):
    if h == H - 1 and w == W - 1:
        return dp[h][w]
    for aa in a:
        if 0 <= h + aa <= H -1:
            if grid[h+aa][w]:
                grid[h+aa][w] = 0
                dp[h+aa][w] = dp[h][w] + 1
                Q.append([h+aa,w])
        if 0 <= w + aa <= W - 1:
            if grid[h][w+aa]:
                grid[h][w+aa] = 0
                dp[h][w+aa] = dp[h][w] + 1
                Q.append([h,w + aa])
    if len(Q) == 0:
        return -1
    else:
        nexth,nextw = Q.pop(0)
        return bfs(grid,nexth,nextw,Q)
queue = []
if Grid[0][0]:
    ans = bfs(Grid,0,0,queue)
    if ans == -1:
        print(-1)
    else:
        print(H*W - ans - 1 - black)
else:
    print(-1)


Fixed submission:
H,W = map(int,input().split())
Grid = [[1 if g == "." else 0 for g in input()] for _ in range(H)]
dp = [[10**5]*(W) for _ in range(H)]
dp[0][0] = 0
black = 0
flag = Grid[0][0]

for g in Grid:
    for gg in g:
        if not(gg):
            black += 1

a = [-1,1]

import sys
sys.setrecursionlimit(10**4)
def bfs(grid,h,w,Q):
    if h == H - 1 and w == W - 1:
        return dp[h][w]
    for aa in a:
        if 0 <= h + aa <= H -1:
            if grid[h+aa][w]:
                grid[h+aa][w] = 0
                dp[h+aa][w] = dp[h][w] + 1
                Q.append([h+aa,w])
        if 0 <= w + aa <= W - 1:
            if grid[h][w+aa]:
                grid[h][w+aa] = 0
                dp[h][w+aa] = dp[h][w] + 1
                Q.append([h,w + aa])
    if len(Q) == 0:
        return -1
    else:
        nexth,nextw = Q.pop(0)
        return bfs(grid,nexth,nextw,Q)
queue = []
Grid[0][0] = 0
if  flag:
    ans = bfs(Grid,0,0,queue)
    if ans == -1:
        print(-1)
    else:
        print(H*W - ans - 1 - black)
else:
    print(-1)

Buggy python submission (verdict: Runtime Error):
H,W = map(int,input().split())
Grid = [[1 if g == "." else 0 for g in input()] for _ in range(H)]
dp = [[10**9]*(W) for _ in range(H)]
dp[0][0] = 0
black = 0

for g in Grid:
    for gg in g:
        if not(gg):
            black += 1

a = [-1,1]
def bfs(grid,h,w,Q):
    if h == H - 1 and w == W - 1:
        return dp[h][w]
    for aa in a:
        if 0 <= h + aa <= H -1:
            if grid[h+aa][w]:
                grid[h+aa][w] = 0
                dp[h+aa][w] = dp[h][w] + 1
                Q.append([h+aa,w])
        if 0 <= w + aa <= W - 1:
            if grid[h][w+aa]:
                grid[h][w+aa] = 0
                dp[h][w+aa] = dp[h][w] + 1
                Q.append([h,w + aa])
    if len(Q) == 0:
        return -1
    else:
        nexth,nextw = Q.pop(0)
        return bfs(grid,nexth,nextw,Q)
queue = []
if Grid[0][0]:
    print(H*W - bfs(Grid,0,0,queue) - 1 - black)
else:
    print(-1)


Fixed submission:
H,W = map(int,input().split())
Grid = [[1 if g == "." else 0 for g in input()] for _ in range(H)]
dp = [[10**5]*(W) for _ in range(H)]
dp[0][0] = 0
black = 0
flag = Grid[0][0]

for g in Grid:
    for gg in g:
        if not(gg):
            black += 1

a = [-1,1]

import sys
sys.setrecursionlimit(10**4)
def bfs(grid,h,w,Q):
    if h == H - 1 and w == W - 1:
        return dp[h][w]
    for aa in a:
        if 0 <= h + aa <= H -1:
            if grid[h+aa][w]:
                grid[h+aa][w] = 0
                dp[h+aa][w] = dp[h][w] + 1
                Q.append([h+aa,w])
        if 0 <= w + aa <= W - 1:
            if grid[h][w+aa]:
                grid[h][w+aa] = 0
                dp[h][w+aa] = dp[h][w] + 1
                Q.append([h,w + aa])
    if len(Q) == 0:
        return -1
    else:
        nexth,nextw = Q.pop(0)
        return bfs(grid,nexth,nextw,Q)
queue = []
Grid[0][0] = 0
if  flag:
    ans = bfs(Grid,0,0,queue)
    if ans == -1:
        print(-1)
    else:
        print(H*W - ans - 1 - black)
else:
    print(-1)