Buggy python submission (verdict: Runtime Error):
import sys
from collections import deque

def bfs(maze, visited):
    try:
        sy,sx=0,0
        gy,gx=H-1,W-1
        queue = deque([[sy, sx]])
        visited[sy][sx] = 0
        while queue:
            y, x = queue.popleft()
            if [y, x] == [gy, gx]:
                return visited[y][x]

            p=[]
            if x>0 : p.append([0,-1])
            if x<W-1: p.append([0,1])
            if y>0: p.append([-1,0])
            if y<H-1: p.append([1,0])
            for j, k in p:
                new_y, new_x = y+j, x+k
                if maze[new_y][new_x] == "." and \
                    visited[new_y][new_x] == -1:
                    visited[new_y][new_x] = visited[y][x] + 1
                    queue.append([new_y, new_x])

    except RuntimeError:
        print(-1)
        sys.exit()


H,W=map(int,input().split())
m=[input() for i in range(H)]

ans=0
for i in range(H):
    for j in range(W):
        if m[i][j]==".": ans+=1

visited=[[-1]*W for i in range(H)]
try:
    print(ans-bfs(m,visited)-1)
except RuntimeError:
    print(-1)
    sys.exit()

Fixed submission:
import sys
from collections import deque

def bfs(maze, visited):
    try:
        sy,sx=0,0
        gy,gx=H-1,W-1
        queue = deque([[sy, sx]])
        visited[sy][sx] = 0
        while queue:
            y, x = queue.popleft()
            if [y, x] == [gy, gx]:
                return visited[y][x]

            p=[]
            if x>0 : p.append([0,-1])
            if x<W-1: p.append([0,1])
            if y>0: p.append([-1,0])
            if y<H-1: p.append([1,0])
            for j, k in p:
                new_y, new_x = y+j, x+k
                if maze[new_y][new_x] == "." and \
                    visited[new_y][new_x] == -1:
                    visited[new_y][new_x] = visited[y][x] + 1
                    queue.append([new_y, new_x])
        return -1

    except RuntimeError:
        print(-1)
        sys.exit()


H,W=map(int,input().split())
m=[input() for i in range(H)]

ans=0
for i in range(H):
    for j in range(W):
        if m[i][j]==".": ans+=1

visited=[[-1]*W for i in range(H)]
p=bfs(m,visited)
print( p if p==-1 else ans-p-1)

Buggy python submission (verdict: Runtime Error):
import sys
from collections import deque

def bfs(maze, visited):
    try:
        sy,sx=0,0
        gy,gx=H-1,W-1
        queue = deque([[sy, sx]])
        visited[sy][sx] = 0
        while queue:
            y, x = queue.popleft()
            if [y, x] == [gy, gx]:
                return visited[y][x]

            p=[]
            if x>0 : p.append([0,-1])
            if x<W-1: p.append([0,1])
            if y>0: p.append([-1,0])
            if y<H-1: p.append([1,0])
            for j, k in p:
                new_y, new_x = y+j, x+k
                if maze[new_y][new_x] == "." and \
                    visited[new_y][new_x] == -1:
                    visited[new_y][new_x] = visited[y][x] + 1
                    queue.append([new_y, new_x])

    except RuntimeError:
        print(-1)


H,W=map(int,input().split())
m=[input() for i in range(H)]

ans=0
for i in range(H):
    for j in range(W):
        if m[i][j]==".": ans+=1

visited=[[-1]*W for i in range(H)]
try:
    print(ans-bfs(m,visited)-1)
except RuntimeError:
    print(-1)

Fixed submission:
import sys
from collections import deque

def bfs(maze, visited):
    try:
        sy,sx=0,0
        gy,gx=H-1,W-1
        queue = deque([[sy, sx]])
        visited[sy][sx] = 0
        while queue:
            y, x = queue.popleft()
            if [y, x] == [gy, gx]:
                return visited[y][x]

            p=[]
            if x>0 : p.append([0,-1])
            if x<W-1: p.append([0,1])
            if y>0: p.append([-1,0])
            if y<H-1: p.append([1,0])
            for j, k in p:
                new_y, new_x = y+j, x+k
                if maze[new_y][new_x] == "." and \
                    visited[new_y][new_x] == -1:
                    visited[new_y][new_x] = visited[y][x] + 1
                    queue.append([new_y, new_x])
        return -1

    except RuntimeError:
        print(-1)
        sys.exit()


H,W=map(int,input().split())
m=[input() for i in range(H)]

ans=0
for i in range(H):
    for j in range(W):
        if m[i][j]==".": ans+=1

visited=[[-1]*W for i in range(H)]
p=bfs(m,visited)
print( p if p==-1 else ans-p-1)

Buggy python submission (verdict: Runtime Error):
import sys
from collections import deque

def bfs(maze, visited):
    try:
        sy,sx=0,0
        gy,gx=H-1,W-1
        queue = deque([[sy, sx]])
        visited[sy][sx] = 0
        while queue:
            y, x = queue.popleft()
            if [y, x] == [gy, gx]:
                return visited[y][x]

            p=[]
            if x>0 : p.append([0,-1])
            if x<W-1: p.append([0,1])
            if y>0: p.append([-1,0])
            if y<H-1: p.append([1,0])
            for j, k in p:
                new_y, new_x = y+j, x+k
                if maze[new_y][new_x] == "." and \
                    visited[new_y][new_x] == -1:
                    visited[new_y][new_x] = visited[y][x] + 1
                    queue.append([new_y, new_x])
    except RuntimeError:
        print(-1)


H,W=map(int,input().split())
m=[input() for i in range(H)]

ans=0
for i in range(H):
    for j in range(W):
        if m[i][j]==".": ans+=1

visited=[[-1]*W for i in range(H)]
print(ans-bfs(m,visited)-1)

Fixed submission:
import sys
from collections import deque

def bfs(maze, visited):
    try:
        sy,sx=0,0
        gy,gx=H-1,W-1
        queue = deque([[sy, sx]])
        visited[sy][sx] = 0
        while queue:
            y, x = queue.popleft()
            if [y, x] == [gy, gx]:
                return visited[y][x]

            p=[]
            if x>0 : p.append([0,-1])
            if x<W-1: p.append([0,1])
            if y>0: p.append([-1,0])
            if y<H-1: p.append([1,0])
            for j, k in p:
                new_y, new_x = y+j, x+k
                if maze[new_y][new_x] == "." and \
                    visited[new_y][new_x] == -1:
                    visited[new_y][new_x] = visited[y][x] + 1
                    queue.append([new_y, new_x])
        return -1

    except RuntimeError:
        print(-1)
        sys.exit()


H,W=map(int,input().split())
m=[input() for i in range(H)]

ans=0
for i in range(H):
    for j in range(W):
        if m[i][j]==".": ans+=1

visited=[[-1]*W for i in range(H)]
p=bfs(m,visited)
print( p if p==-1 else ans-p-1)

Buggy python submission (verdict: Runtime Error):
import sys
from collections import deque

def bfs(maze, visited):
    try:
        sy,sx=0,0
        gy,gx=H-1,W-1
        queue = deque([[sy, sx]])
        visited[sy][sx] = 0
        while queue:
            y, x = queue.popleft()
            if [y, x] == [gy, gx]:
                return visited[y][x]

            p=[]
            if x>0 : p.append([0,-1])
            if x<W-1: p.append([0,1])
            if y>0: p.append([-1,0])
            if y<H-1: p.append([1,0])
            for j, k in p:
                new_y, new_x = y+j, x+k
                if maze[new_y][new_x] == "." and \
                    visited[new_y][new_x] == -1:
                    visited[new_y][new_x] = visited[y][x] + 1
                    queue.append([new_y, new_x])
    except RuntimeError:
        return -1


H,W=map(int,input().split())
m=[input() for i in range(H)]

ans=0
for i in range(H):
    for j in range(W):
        if m[i][j]==".": ans+=1

visited=[[-1]*W for i in range(H)]
p=bfs(m,visited)
print(p if p==-1 else ans-p-1)

Fixed submission:
import sys
from collections import deque

def bfs(maze, visited):
    try:
        sy,sx=0,0
        gy,gx=H-1,W-1
        queue = deque([[sy, sx]])
        visited[sy][sx] = 0
        while queue:
            y, x = queue.popleft()
            if [y, x] == [gy, gx]:
                return visited[y][x]

            p=[]
            if x>0 : p.append([0,-1])
            if x<W-1: p.append([0,1])
            if y>0: p.append([-1,0])
            if y<H-1: p.append([1,0])
            for j, k in p:
                new_y, new_x = y+j, x+k
                if maze[new_y][new_x] == "." and \
                    visited[new_y][new_x] == -1:
                    visited[new_y][new_x] = visited[y][x] + 1
                    queue.append([new_y, new_x])
        return -1

    except RuntimeError:
        print(-1)
        sys.exit()


H,W=map(int,input().split())
m=[input() for i in range(H)]

ans=0
for i in range(H):
    for j in range(W):
        if m[i][j]==".": ans+=1

visited=[[-1]*W for i in range(H)]
p=bfs(m,visited)
print( p if p==-1 else ans-p-1)

Buggy python submission (verdict: Runtime Error):
import sys
from collections import deque

def bfs(maze, visited):
    sy,sx=0,0
    gy,gx=H-1,W-1
    queue = deque([[sy, sx]])
    visited[sy][sx] = 0
    while queue:
        y, x = queue.popleft()
        if [y, x] == [gy, gx]:
            return visited[y][x]

        p=[]
        if x>0 : p.append([0,-1])
        if x<W-1: p.append([0,1])
        if y>0: p.append([-1,0])
        if y<H-1: p.append([1,0])
        for j, k in p:
            new_y, new_x = y+j, x+k
            if maze[new_y][new_x] == "." and \
                visited[new_y][new_x] == -1:
                visited[new_y][new_x] = visited[y][x] + 1
                queue.append([new_y, new_x])


H,W=map(int,input().split())
m=[input() for i in range(H)]

ans=0
for i in range(H):
    for j in range(W):
        if m[i][j]==".": ans+=1

visited=[[-1]*W for i in range(H)]
print(ans-bfs(m,visited)-1)

Fixed submission:
import sys
from collections import deque

def bfs(maze, visited):
    try:
        sy,sx=0,0
        gy,gx=H-1,W-1
        queue = deque([[sy, sx]])
        visited[sy][sx] = 0
        while queue:
            y, x = queue.popleft()
            if [y, x] == [gy, gx]:
                return visited[y][x]

            p=[]
            if x>0 : p.append([0,-1])
            if x<W-1: p.append([0,1])
            if y>0: p.append([-1,0])
            if y<H-1: p.append([1,0])
            for j, k in p:
                new_y, new_x = y+j, x+k
                if maze[new_y][new_x] == "." and \
                    visited[new_y][new_x] == -1:
                    visited[new_y][new_x] = visited[y][x] + 1
                    queue.append([new_y, new_x])
        return -1

    except RuntimeError:
        print(-1)
        sys.exit()


H,W=map(int,input().split())
m=[input() for i in range(H)]

ans=0
for i in range(H):
    for j in range(W):
        if m[i][j]==".": ans+=1

visited=[[-1]*W for i in range(H)]
p=bfs(m,visited)
print( p if p==-1 else ans-p-1)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
inf=10**10

def dijkstra(s,n,cost):
    #始点sから各頂点への最短距離
    #n:頂点数,　w:辺の数, cost[u][v] : 辺uvのコスト(存在しないときはinf)
    d = [float("inf")] * n
    used = [False] * n
    for i in range(H):
        for j in range(W):
            if x[i][j]==inf: used[i*W+j]=True
    d[s] = 0
    
    while True:
        v = -1
        #まだ使われてない頂点の中から最小の距離のものを探す
        for i in range(n):
            if (not used[i]) and (v == -1):
               v = i
            elif (not used[i]) and d[i] < d[v]:
                v = i
        if v == -1:
               break
        used[v] = True

        p=[]    
        if v>W-1: p.append(v-W)
        if v+W<H*W: p.append(v+W)
        if v%W>0: p.append(v-1)
        if v%W<W-1: p.append(v+1)
        for j in range(n):
               d[j] = min(d[j],d[v]+cost[v][j])
    return d


def f(s):
    r=[]
    for j in range(W):
        if s[j]=="#": r.append(inf)
        elif s[j]==".": r.append(0)
    return r

H,W=map(int,input().split())
x=[f(input()) for i in range(H)]

cost = [[float("inf") for i in range(H*W)] for i in range(H*W)] 
for i in range(H*W):
    for j in range(H*W):
        if x[i//W][i%W]==inf or x[j//W][j%W]==inf: continue
        if abs(i-j)==W: cost[i][j],cost[j][i]=1,1
        elif i-j==1 and i%W!=0: cost[i][j],cost[j][i]=1,1
        elif j-i==1 and j%W!=0: cost[i][j],cost[j][i]=1,1

ans=0
for i in range(H):
    for j in range(W):
        if x[i][j]==0: ans+=1

ans-=dijkstra(0,H*W,cost)[H*W-1]+1
print(ans if ans>=0 else -1)

Fixed submission:
import sys
from collections import deque

def bfs(maze, visited):
    try:
        sy,sx=0,0
        gy,gx=H-1,W-1
        queue = deque([[sy, sx]])
        visited[sy][sx] = 0
        while queue:
            y, x = queue.popleft()
            if [y, x] == [gy, gx]:
                return visited[y][x]

            p=[]
            if x>0 : p.append([0,-1])
            if x<W-1: p.append([0,1])
            if y>0: p.append([-1,0])
            if y<H-1: p.append([1,0])
            for j, k in p:
                new_y, new_x = y+j, x+k
                if maze[new_y][new_x] == "." and \
                    visited[new_y][new_x] == -1:
                    visited[new_y][new_x] = visited[y][x] + 1
                    queue.append([new_y, new_x])
        return -1

    except RuntimeError:
        print(-1)
        sys.exit()


H,W=map(int,input().split())
m=[input() for i in range(H)]

ans=0
for i in range(H):
    for j in range(W):
        if m[i][j]==".": ans+=1

visited=[[-1]*W for i in range(H)]
p=bfs(m,visited)
print( p if p==-1 else ans-p-1)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
sys.setrecursionlimit(1000000)
inf=10**10

def dijkstra(s,n,cost):
    #始点sから各頂点への最短距離
    #n:頂点数,　w:辺の数, cost[u][v] : 辺uvのコスト(存在しないときはinf)
    d = [float("inf")] * n
    used = [False] * n
    d[s] = 0
    
    while True:
        v = -1
        #まだ使われてない頂点の中から最小の距離のものを探す
        for i in range(n):
            if (not used[i]) and (v == -1):
               v = i
            elif (not used[i]) and d[i] < d[v]:
                v = i
        if v == -1:
               break
        used[v] = True

        p=[]    
        if v>W-1: p.append(v-W)
        if v+W<H*W: p.append(v+W)
        if v%W>0: p.append(v-1)
        if v%W<W-1: p.append(v+1)
        for j in range(n):
               d[j] = min(d[j],d[v]+cost[v][j])
    return d


def f(s):
    r=[]
    for j in range(W):
        if s[j]=="#": r.append(inf)
        elif s[j]==".": r.append(0)
    return r

H,W=map(int,input().split())
x=[f(input()) for i in range(H)]

cost = [[float("inf") for i in range(H*W)] for i in range(H*W)] 
for i in range(H*W):
    for j in range(H*W):
        if x[i//W][i%W]==inf or x[j//W][j%W]==inf: continue
        if abs(i-j)==W: cost[i][j],cost[j][i]=1,1
        elif i-j==1 and i%W!=0: cost[i][j],cost[j][i]=1,1
        elif j-i==1 and j%W!=0: cost[i][j],cost[j][i]=1,1

ans=0
for i in range(H):
    for j in range(W):
        if x[i][j]==0: ans+=1

ans-=dijkstra(0,H*W,cost)[H*W-1]+1
print(ans if ans>=0 else -1)

Fixed submission:
import sys
from collections import deque

def bfs(maze, visited):
    try:
        sy,sx=0,0
        gy,gx=H-1,W-1
        queue = deque([[sy, sx]])
        visited[sy][sx] = 0
        while queue:
            y, x = queue.popleft()
            if [y, x] == [gy, gx]:
                return visited[y][x]

            p=[]
            if x>0 : p.append([0,-1])
            if x<W-1: p.append([0,1])
            if y>0: p.append([-1,0])
            if y<H-1: p.append([1,0])
            for j, k in p:
                new_y, new_x = y+j, x+k
                if maze[new_y][new_x] == "." and \
                    visited[new_y][new_x] == -1:
                    visited[new_y][new_x] = visited[y][x] + 1
                    queue.append([new_y, new_x])
        return -1

    except RuntimeError:
        print(-1)
        sys.exit()


H,W=map(int,input().split())
m=[input() for i in range(H)]

ans=0
for i in range(H):
    for j in range(W):
        if m[i][j]==".": ans+=1

visited=[[-1]*W for i in range(H)]
p=bfs(m,visited)
print( p if p==-1 else ans-p-1)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
sys.setrecursionlimit(1000000)
inf=10**10

def dijkstra(s,n,cost):
    #始点sから各頂点への最短距離
    #n:頂点数,　w:辺の数, cost[u][v] : 辺uvのコスト(存在しないときはinf)
    d = [float("inf")] * n
    used = [False] * n
    d[s] = 0
    
    while True:
        v = -1
        #まだ使われてない頂点の中から最小の距離のものを探す
        for i in range(n):
            if (not used[i]) and (v == -1):
               v = i
            elif (not used[i]) and d[i] < d[v]:
                v = i
        if v == -1:
               break
        used[v] = True
               
        for j in range(n):
               d[j] = min(d[j],d[v]+cost[v][j])
    return d


def f(s):
    r=[]
    for j in range(W):
        if s[j]=="#": r.append(inf)
        elif s[j]==".": r.append(0)
    return r

H,W=map(int,input().split())
x=[f(input()) for i in range(H)]

cost = [[float("inf") for i in range(H*W)] for i in range(H*W)] 
for i in range(H*W):
    for j in range(H*W):
        if x[i//W][i%W]==inf or x[j//W][j%W]==inf: continue
        if abs(i-j)==W: cost[i][j],cost[j][i]=1,1
        elif i-j==1 and i%W!=0: cost[i][j],cost[j][i]=1,1
        elif j-i==1 and j%W!=0: cost[i][j],cost[j][i]=1,1

ans=0
for i in range(H):
    for j in range(W):
        if x[i][j]==0: ans+=1

ans-=dijkstra(0,H*W,cost)[H*W-1]+1
print(ans if ans>=0 else -1)

Fixed submission:
import sys
from collections import deque

def bfs(maze, visited):
    try:
        sy,sx=0,0
        gy,gx=H-1,W-1
        queue = deque([[sy, sx]])
        visited[sy][sx] = 0
        while queue:
            y, x = queue.popleft()
            if [y, x] == [gy, gx]:
                return visited[y][x]

            p=[]
            if x>0 : p.append([0,-1])
            if x<W-1: p.append([0,1])
            if y>0: p.append([-1,0])
            if y<H-1: p.append([1,0])
            for j, k in p:
                new_y, new_x = y+j, x+k
                if maze[new_y][new_x] == "." and \
                    visited[new_y][new_x] == -1:
                    visited[new_y][new_x] = visited[y][x] + 1
                    queue.append([new_y, new_x])
        return -1

    except RuntimeError:
        print(-1)
        sys.exit()


H,W=map(int,input().split())
m=[input() for i in range(H)]

ans=0
for i in range(H):
    for j in range(W):
        if m[i][j]==".": ans+=1

visited=[[-1]*W for i in range(H)]
p=bfs(m,visited)
print( p if p==-1 else ans-p-1)