Buggy python submission (verdict: Runtime Error):
from collections import deque
h,w=map(int,input().split())
S=[input() for _ in range(h)]
inf=float('inf')
ans=0
for i in range(h):
    for j in range(w):
        if S[i][j]!='#':
            dp=[[inf for _ in range(w)] for _ in range(h)]
            dp[i][j]=0
            que=deque([(i,j)])
        while que:
            si,sj=que.popleft()
            for ni,nj in [(si+1,sj),(si-1,sj),(si,sj+1),(si,sj-1)]:
                if 0<=ni<h and 0<=nj<w and S[ni][nj]!='#':
                    if dp[ni][nj]>dp[si][sj]+1:
                        dp[ni][nj]=dp[si][sj]+1
                        ans=max(ans,dp[si][sj]+1)
                        que.append((ni,nj))
print(ans)


Fixed submission:
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
 
from collections import deque
 
H,W = map(int,readline().split())
H += 2; W += 2
grid = '#' * W
for _ in range(H-2):
    grid += '#' + readline().rstrip().decode() + '#'
grid += '#' * W
 
def bfs(start):
    INF = 10 ** 9
    dist = [INF] * (H*W)
    dist[start] = 0
    q = deque([start])
    while q:
        v = q.popleft()
        dv = dist[v]
        for move in (-1,1,W,-W):
            w = v + move
            if grid[w] == '#':
                continue
            dw = dv + 1
            if dw >= dist[w]:
                continue
            dist[w] = dw
            q.append(w)
    return max(x for x in dist if x < INF)
 
answer = max(bfs(v) for v in range(H*W) if grid[v] != '#')
print(answer)

Buggy python submission (verdict: Runtime Error):
from collections import deque
h,w=map(int,input().split())
S=[input() for _ in range(h)]
inf=float("inf")
ans=0
for i in range(h):
   for j in range(w):
      if S[i][j]=="#":
         continue
      else:
         DP=[[inf for _ in range(w)]for _ in range(h)]
         DP[i][j]=0
         que=deque([(i,j)])
         while que:
            si,sj=que.popleft()
            for ni,nj in [(si+1,sj)(si-1,sj)(si,sj+1)(si,sj-1)]:
               if 0<=ni<h and 0<=nj<w and S[ni][nj]!="#":
                  if DP[ni][nj]>DP[si][sj]+1:
                     DP[ni][nj]=DP[si][sj]+1
                     que.append((ni,nj))
                     ans=max(ans,DP[si][sj]+1)
print(ans)
              

Fixed submission:
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
 
from collections import deque
 
H,W = map(int,readline().split())
H += 2; W += 2
grid = '#' * W
for _ in range(H-2):
    grid += '#' + readline().rstrip().decode() + '#'
grid += '#' * W
 
def bfs(start):
    INF = 10 ** 9
    dist = [INF] * (H*W)
    dist[start] = 0
    q = deque([start])
    while q:
        v = q.popleft()
        dv = dist[v]
        for move in (-1,1,W,-W):
            w = v + move
            if grid[w] == '#':
                continue
            dw = dv + 1
            if dw >= dist[w]:
                continue
            dist[w] = dw
            q.append(w)
    return max(x for x in dist if x < INF)
 
answer = max(bfs(v) for v in range(H*W) if grid[v] != '#')
print(answer)

Buggy python submission (verdict: Runtime Error):
from collections import deque
h,w=map(int,input().split())
S=[input() for _ range(h)]
inf=float("inf")
ans=0
for i in range(h):
   for j in range(w):
      if S[i][j]=="#":
         continue
      else:
         DP=[[inf for _ in range(w)]for _ in range(h)]
         DP[i][j]=0
         que=deque([(i,j)])
         while que:
            si,sj=que.popleft()
            for ni,nj in [(si+1,sj)(si-1,sj)(si,sj+1)(si,sj-1)]:
               if 0<=ni<h and 0<=nj<w and S[ni][nj]!="#":
                  if DP[ni][nj]>DP[si][sj]+1:
                     DP[ni][nj]=DP[si][sj]+1
                     que.append((ni,nj))
                     ans=max(ans,DP[si][sj]+1)
print(ans)
                   

Fixed submission:
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
 
from collections import deque
 
H,W = map(int,readline().split())
H += 2; W += 2
grid = '#' * W
for _ in range(H-2):
    grid += '#' + readline().rstrip().decode() + '#'
grid += '#' * W
 
def bfs(start):
    INF = 10 ** 9
    dist = [INF] * (H*W)
    dist[start] = 0
    q = deque([start])
    while q:
        v = q.popleft()
        dv = dist[v]
        for move in (-1,1,W,-W):
            w = v + move
            if grid[w] == '#':
                continue
            dw = dv + 1
            if dw >= dist[w]:
                continue
            dist[w] = dw
            q.append(w)
    return max(x for x in dist if x < INF)
 
answer = max(bfs(v) for v in range(H*W) if grid[v] != '#')
print(answer)

Buggy python submission (verdict: Runtime Error):
from collections import deque
h,w=map(int,input().split())
S=[input() for _ range(h)]
inf=float("inf")
ans=0
for i in range(h):
   for j in range(w):
      if S[i][j]=="#":
         continue
      else:
         DP=[[inf for _ in range(w)]for _ in range(h)]
         D[i][j]=0
         que=deque([(i,j)])
         while que:
            si,sj=que.popleft()
            for ni,nj in [(si+1,sj)(si-1,sj)(si,sj+1)(si,sj-1)]:
               if 0<=ni<h and 0<=nj<w and S[ni][nj]!="#":
                  if D[ni][nj]>D[si][sj]+1:
                     D[ni][nj]=D[si][sj]+1
                     que.append((ni,nj))
                     ans=max(ans,D[si][sj]+1)
print(ans)

Fixed submission:
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
 
from collections import deque
 
H,W = map(int,readline().split())
H += 2; W += 2
grid = '#' * W
for _ in range(H-2):
    grid += '#' + readline().rstrip().decode() + '#'
grid += '#' * W
 
def bfs(start):
    INF = 10 ** 9
    dist = [INF] * (H*W)
    dist[start] = 0
    q = deque([start])
    while q:
        v = q.popleft()
        dv = dist[v]
        for move in (-1,1,W,-W):
            w = v + move
            if grid[w] == '#':
                continue
            dw = dv + 1
            if dw >= dist[w]:
                continue
            dist[w] = dw
            q.append(w)
    return max(x for x in dist if x < INF)
 
answer = max(bfs(v) for v in range(H*W) if grid[v] != '#')
print(answer)

Buggy python submission (verdict: Runtime Error):
from collections import deque
 
H,W = map(int,readline().split())
H += 2; W += 2
grid = '#' * W
for _ in range(H-2):
    grid += '#' + readline().rstrip().decode() + '#'
grid += '#' * W
 
def bfs(start):
    INF = 10 ** 9
    dist = [INF] * (H*W)
    dist[start] = 0
    q = deque([start])
    while q:
        v = q.popleft()
        dv = dist[v]
        for move in (-1,1,W,-W):
            w = v + move
            if grid[w] == '#':
                continue
            dw = dv + 1
            if dw >= dist[w]:
                continue
            dist[w] = dw
            q.append(w)
    return max(x for x in dist if x < INF)
 
answer = max(bfs(v) for v in range(H*W) if grid[v] != '#')
print(answer)

Fixed submission:
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
 
from collections import deque
 
H,W = map(int,readline().split())
H += 2; W += 2
grid = '#' * W
for _ in range(H-2):
    grid += '#' + readline().rstrip().decode() + '#'
grid += '#' * W
 
def bfs(start):
    INF = 10 ** 9
    dist = [INF] * (H*W)
    dist[start] = 0
    q = deque([start])
    while q:
        v = q.popleft()
        dv = dist[v]
        for move in (-1,1,W,-W):
            w = v + move
            if grid[w] == '#':
                continue
            dw = dv + 1
            if dw >= dist[w]:
                continue
            dist[w] = dw
            q.append(w)
    return max(x for x in dist if x < INF)
 
answer = max(bfs(v) for v in range(H*W) if grid[v] != '#')
print(answer)