Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

H, W = map(int, input().split())
# sx, sy = map(int, input().split())
# gx, gy = map(int, input().split())
# sx, sy, gx, gy = sx-1, sy-1, gx-1, gy-1
c = [input() for i in range(H)]
INF = 10**9
def bfs():
    dist = [[INF for i in range(W)] for j in range(H)]
    dx = [1, 0, -1, 0]
    dy = [0, 1, 0, -1]
    q = deque()
    q.append([sx, sy])
    dist[sx][sy] = 0
    while q:
        p = q.popleft()
        if p[0] == gx and p[1] == gy:
            break
        for i in range(4):
            nx = p[0] + dx[i]
            ny = p[1] + dy[i]
            if 0 <= nx and nx < H and 0 <= ny and ny < W:
                if c[nx][ny] != '#' and dist[nx][ny] == INF:
                    q.append([nx, ny])
                    dist[nx][ny] = dist[p[0]][p[1]] + 1
    return dist[gx][gy]

ans = -1
for i in range(H):
    for j in range(W):
        for k in range(H):
            for l in range(W):
                sx, sy = i, j
                gx, gy = k, l
                if c[sx][sy] == '#' or c[gx][gy] == '#':
                    continue
                if bfs() == INF:
                    continue
                ans = max(ans, bfs())
print(ans)

Fixed submission:
from collections import deque

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

INF = -1

def bfs():
    dist = [[INF for i in range(W)] for j in range(H)]
    dx = [1, 0, -1, 0]
    dy = [0, 1, 0, -1]
    q = deque()
    q.append([sx, sy])
    dist[sx][sy] = 0
    while q:
        p = q.popleft()
        # if p[0] == gx and p[1] == gy:
        #     break
        for i in range(4):
            nx = p[0] + dx[i]
            ny = p[1] + dy[i]
            if 0 <= nx and nx < H and 0 <= ny and ny < W:
                if c[nx][ny] != '#' and dist[nx][ny] == INF:
                    q.append([nx, ny])
                    dist[nx][ny] = dist[p[0]][p[1]] + 1
    ret = -1
    for i in range(H):
        ret = max(ret, max(dist[i]))
    return ret

ans = -1
for i in range(H):
    for j in range(W):
            sx, sy = i, j
            if c[sx][sy] == '#':
                continue
            ans = max(ans, bfs())
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

H, W = map(int, input().split())
# sx, sy = map(int, input().split())
# gx, gy = map(int, input().split())
# sx, sy, gx, gy = sx-1, sy-1, gx-1, gy-1
c = [input() for i in range(H)]
INF = 10**9
def bfs():
    dist = [[INF for i in range(W)] for j in range(H)]
    dx = [1, 0, -1, 0]
    dy = [0, 1, 0, -1]
    q = deque()
    q.append([sx, sy])
    dist[sx][sy] = 0
    while q:
        p = q.popleft()
        if p[0] == gx and p[1] == gy:
            break
        for i in range(4):
            nx = p[0] + dx[i]
            ny = p[1] + dy[i]
            if 0 <= nx and nx < H and 0 <= ny and ny < W:
                if c[nx][ny] != '#' and dist[nx][ny] == INF:
                    q.append([nx, ny])
                    dist[nx][ny] = dist[p[0]][p[1]] + 1
    return dist[gx][gy]

ans = -1
for i in range(H):
    for j in range(W):
        for k in range(H):
            for l in range(W):
                sx, sy = i, j
                gx, gy = k, l
                if c[sx][sy] == '#' or c[gx][gy] == '#':
                    continue
                if bfs() == INF:
                    continue
                ans = max(ans, bfs())
print(ans)

Fixed submission:
from collections import deque

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

INF = -1

def bfs():
    dist = [[INF for i in range(W)] for j in range(H)]
    dx = [1, 0, -1, 0]
    dy = [0, 1, 0, -1]
    q = deque()
    q.append([sx, sy])
    dist[sx][sy] = 0
    while q:
        p = q.popleft()
        # if p[0] == gx and p[1] == gy:
        #     break
        for i in range(4):
            nx = p[0] + dx[i]
            ny = p[1] + dy[i]
            if 0 <= nx and nx < H and 0 <= ny and ny < W:
                if c[nx][ny] != '#' and dist[nx][ny] == INF:
                    q.append([nx, ny])
                    dist[nx][ny] = dist[p[0]][p[1]] + 1
    ret = -1
    for i in range(H):
        ret = max(ret, max(dist[i]))
    return ret

ans = -1
for i in range(H):
    for j in range(W):
            sx, sy = i, j
            if c[sx][sy] == '#':
                continue
            ans = max(ans, bfs())
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

H, W = map(int, input().split())
# sx, sy = map(int, input().split())
# gx, gy = map(int, input().split())
# sx, sy, gx, gy = sx-1, sy-1, gx-1, gy-1
c = [input() for i in range(H)]
INF = 10**9
def bfs():
    dist = [[INF for i in range(W)] for j in range(H)]
    dx = [1, 0, -1, 0]
    dy = [0, 1, 0, -1]
    q = deque()
    q.append([sx, sy])
    dist[sx][sy] = 0
    while q:
        p = q.popleft()
        if p[0] == gx and p[1] == gy:
            break
        for i in range(4):
            nx = p[0] + dx[i]
            ny = p[1] + dy[i]
            if 0 <= nx and nx < H and 0 <= ny and ny < W:
                if c[nx][ny] != '#' and dist[nx][ny] == INF:
                    q.append([nx, ny])
                    dist[nx][ny] = dist[p[0]][p[1]] + 1
    return dist[gx][gy]

ans = -1
can = []
for i in range(H):
    for j in range(W):
        for k in range(H):
            for l in range(W):
                sx, sy = i, j
                gx, gy = k, l
                if c[sx][sy] == '#' or c[gx][gy] == '#':
                    continue
                can.append((sx, sy, gx, gy))

for sx, sy, gx, gy in can:
    if bfs() == INF:
        continue
    ans = max(ans, bfs())

print(ans)

Fixed submission:
from collections import deque

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

INF = -1

def bfs():
    dist = [[INF for i in range(W)] for j in range(H)]
    dx = [1, 0, -1, 0]
    dy = [0, 1, 0, -1]
    q = deque()
    q.append([sx, sy])
    dist[sx][sy] = 0
    while q:
        p = q.popleft()
        # if p[0] == gx and p[1] == gy:
        #     break
        for i in range(4):
            nx = p[0] + dx[i]
            ny = p[1] + dy[i]
            if 0 <= nx and nx < H and 0 <= ny and ny < W:
                if c[nx][ny] != '#' and dist[nx][ny] == INF:
                    q.append([nx, ny])
                    dist[nx][ny] = dist[p[0]][p[1]] + 1
    ret = -1
    for i in range(H):
        ret = max(ret, max(dist[i]))
    return ret

ans = -1
for i in range(H):
    for j in range(W):
            sx, sy = i, j
            if c[sx][sy] == '#':
                continue
            ans = max(ans, bfs())
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

H, W = map(int, input().split())
# sx, sy = map(int, input().split())
# gx, gy = map(int, input().split())
# sx, sy, gx, gy = sx-1, sy-1, gx-1, gy-1
c = [input() for i in range(H)]
INF = 10**9
def bfs():
    dist = [[INF for i in range(W)] for j in range(H)]
    dx = [1, 0, -1, 0]
    dy = [0, 1, 0, -1]
    q = deque()
    q.append([sx, sy])
    dist[sx][sy] = 0
    while q:
        p = q.popleft()
        if p[0] == gx and p[1] == gy:
            break
        for i in range(4):
            nx = p[0] + dx[i]
            ny = p[1] + dy[i]
            if 0 <= nx and nx < H and 0 <= ny and ny < W:
                if c[nx][ny] != '#' and dist[nx][ny] == INF:
                    q.append([nx, ny])
                    dist[nx][ny] = dist[p[0]][p[1]] + 1
    return dist[gx][gy]

ans = []
can = []
for i in range(H):
    for j in range(W):
        for k in range(H):
            for l in range(W):
                sx, sy = i, j
                gx, gy = k, l
                if c[sx][sy] == '#' or c[gx][gy] == '#':
                    continue
                can.append((sx, sy, gx, gy))

for sx, sy, gx, gy in can:
    ans.append(bfs())
                
ans = [i for i in ans if i != INF]
print(max(ans))

Fixed submission:
from collections import deque

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

INF = -1

def bfs():
    dist = [[INF for i in range(W)] for j in range(H)]
    dx = [1, 0, -1, 0]
    dy = [0, 1, 0, -1]
    q = deque()
    q.append([sx, sy])
    dist[sx][sy] = 0
    while q:
        p = q.popleft()
        # if p[0] == gx and p[1] == gy:
        #     break
        for i in range(4):
            nx = p[0] + dx[i]
            ny = p[1] + dy[i]
            if 0 <= nx and nx < H and 0 <= ny and ny < W:
                if c[nx][ny] != '#' and dist[nx][ny] == INF:
                    q.append([nx, ny])
                    dist[nx][ny] = dist[p[0]][p[1]] + 1
    ret = -1
    for i in range(H):
        ret = max(ret, max(dist[i]))
    return ret

ans = -1
for i in range(H):
    for j in range(W):
            sx, sy = i, j
            if c[sx][sy] == '#':
                continue
            ans = max(ans, bfs())
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

H, W = map(int, input().split())
# sx, sy = map(int, input().split())
# gx, gy = map(int, input().split())
# sx, sy, gx, gy = sx-1, sy-1, gx-1, gy-1
c = [input() for i in range(H)]
INF = 10**9
def bfs():
    dist = [[INF for i in range(W)] for j in range(H)]
    dx = [1, 0, -1, 0]
    dy = [0, 1, 0, -1]
    q = deque()
    q.append([sx, sy])
    dist[sx][sy] = 0
    while q:
        p = q.popleft()
        if p[0] == gx and p[1] == gy:
            break
        for i in range(4):
            nx = p[0] + dx[i]
            ny = p[1] + dy[i]
            if 0 <= nx and nx < H and 0 <= ny and ny < W:
                if c[nx][ny] != '#' and dist[nx][ny] == INF:
                    q.append([nx, ny])
                    dist[nx][ny] = dist[p[0]][p[1]] + 1
    return dist[gx][gy]

ans = []
for i in range(H):
    for j in range(W):
        for k in range(H):
            for l in range(W):
                sx, sy = i, j
                gx, gy = k, l
                if c[sx][sy] == '#' or c[gx][gy] == '#':
                    continue
                ans.append(bfs())
                
ans = [i for i in ans if i != INF]
print(max(ans))

Fixed submission:
from collections import deque

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

INF = -1

def bfs():
    dist = [[INF for i in range(W)] for j in range(H)]
    dx = [1, 0, -1, 0]
    dy = [0, 1, 0, -1]
    q = deque()
    q.append([sx, sy])
    dist[sx][sy] = 0
    while q:
        p = q.popleft()
        # if p[0] == gx and p[1] == gy:
        #     break
        for i in range(4):
            nx = p[0] + dx[i]
            ny = p[1] + dy[i]
            if 0 <= nx and nx < H and 0 <= ny and ny < W:
                if c[nx][ny] != '#' and dist[nx][ny] == INF:
                    q.append([nx, ny])
                    dist[nx][ny] = dist[p[0]][p[1]] + 1
    ret = -1
    for i in range(H):
        ret = max(ret, max(dist[i]))
    return ret

ans = -1
for i in range(H):
    for j in range(W):
            sx, sy = i, j
            if c[sx][sy] == '#':
                continue
            ans = max(ans, bfs())
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque

H, W = map(int, input().split())
# sx, sy = map(int, input().split())
# gx, gy = map(int, input().split())
# sx, sy, gx, gy = sx-1, sy-1, gx-1, gy-1
c = [input() for i in range(H)]

def bfs():
    dist = [[float('inf') for i in range(W)] for j in range(H)]
    dx = [1, 0, -1, 0]
    dy = [0, 1, 0, -1]
    q = deque()
    q.append([sx, sy])
    dist[sx][sy] = 0
    while q:
        p = q.popleft()
        if p[0] == gx and p[1] == gy:
            break
        for i in range(4):
            nx = p[0] + dx[i]
            ny = p[1] + dy[i]
            if 0 <= nx and nx < H and 0 <= ny and ny < W:
                if c[nx][ny] != '#' and dist[nx][ny] == float('inf'):
                    q.append([nx, ny])
                    dist[nx][ny] = dist[p[0]][p[1]] + 1
    return dist[gx][gy]

ans = []
for i in range(H):
    for j in range(W):
        for k in range(H):
            for l in range(W):
                sx, sy = i, j
                gx, gy = k, l
                if c[sx][sy] == '#' or c[gx][gy] == '#':
                    continue
                ans.append(bfs())
                
ans = [i for i in ans if i != float('inf')]
print(max(ans))

Fixed submission:
from collections import deque

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

INF = -1

def bfs():
    dist = [[INF for i in range(W)] for j in range(H)]
    dx = [1, 0, -1, 0]
    dy = [0, 1, 0, -1]
    q = deque()
    q.append([sx, sy])
    dist[sx][sy] = 0
    while q:
        p = q.popleft()
        # if p[0] == gx and p[1] == gy:
        #     break
        for i in range(4):
            nx = p[0] + dx[i]
            ny = p[1] + dy[i]
            if 0 <= nx and nx < H and 0 <= ny and ny < W:
                if c[nx][ny] != '#' and dist[nx][ny] == INF:
                    q.append([nx, ny])
                    dist[nx][ny] = dist[p[0]][p[1]] + 1
    ret = -1
    for i in range(H):
        ret = max(ret, max(dist[i]))
    return ret

ans = -1
for i in range(H):
    for j in range(W):
            sx, sy = i, j
            if c[sx][sy] == '#':
                continue
            ans = max(ans, bfs())
print(ans)

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

H, W = map(int, input().split())
# sx, sy = map(int, input().split())
# gx, gy = map(int, input().split())
# sx, sy, gx, gy = sx-1, sy-1, gx-1, gy-1
c = [input() for i in range(H)]

dist = [[float('inf') for i in range(W)] for j in range(H)]
dx = [1, 0, -1, 0]
dy = [0, 1, 0, -1]

def bfs():
    q = deque()
    q.append([sx, sy])
    dist[sx][sy] = 0
    while q:
        p = q.popleft()
        if p[0] == gx and p[1] == gy:
            break
        for i in range(4):
            nx = p[0] + dx[i]
            ny = p[1] + dy[i]
            if 0 <= nx and nx < H and 0 <= ny and ny < W:
                if c[nx][ny] != '#' and dist[nx][ny] == float('inf'):
                    q.append([nx, ny])
                    dist[nx][ny] = dist[p[0]][p[1]] + 1
    return dist[gx][gy]

sx, sy, gx, gy = 2, 0, 0, 4
print(bfs())
ans = []
for i in range(H):
    for j in range(W):
        sx, sy = i, j
        for k in range(H):
            for l in range(W):
                gx, gy = k, l
                ans.append(bfs())

# print(ans)
ans = [i for i in ans if i != float('inf')]
print(max(ans))

Fixed submission:
from collections import deque

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

INF = -1

def bfs():
    dist = [[INF for i in range(W)] for j in range(H)]
    dx = [1, 0, -1, 0]
    dy = [0, 1, 0, -1]
    q = deque()
    q.append([sx, sy])
    dist[sx][sy] = 0
    while q:
        p = q.popleft()
        # if p[0] == gx and p[1] == gy:
        #     break
        for i in range(4):
            nx = p[0] + dx[i]
            ny = p[1] + dy[i]
            if 0 <= nx and nx < H and 0 <= ny and ny < W:
                if c[nx][ny] != '#' and dist[nx][ny] == INF:
                    q.append([nx, ny])
                    dist[nx][ny] = dist[p[0]][p[1]] + 1
    ret = -1
    for i in range(H):
        ret = max(ret, max(dist[i]))
    return ret

ans = -1
for i in range(H):
    for j in range(W):
            sx, sy = i, j
            if c[sx][sy] == '#':
                continue
            ans = max(ans, bfs())
print(ans)