Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
def main():
    h,w=map(int,input().split())
    hw=h*w
    maze=[]
    r_append=maze.append
    for i in range(h):
        #r_append=maze.append
        #row=input()
        r_append(input())
    #print(maze)
    #root=[[-1 for i in range(h*w)] for i in range(h*w)]
    root=[0]*(hw)
    ina=[0]*hw
    for i in range(hw):
        root[i]=[-1]*(hw)
        ina[i]=[i]
    
    for i in range(h):
        for j in range(w):
        # print(maze[i][j])
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if maze[i][j]==".":
                if j>0:
                    if maze[i][j-1]!="#":
                        root[now][hidari]=0
                if i+1<h:
                    if maze[i+1][j]!="#":
                        root[now][sita]=0
                if j+1<w:
                    if maze[i][j+1]!="#":
                        root[now][migi]=0
                if 0<i:
                    if maze[i-1][j]!="#":
                        root[now][ue]=0
            else:
                ina[now]=-1
                if j>0:
                    root[now][hidari]=-1
                if i+1<h:
                    root[now][sita]=-1
                if j+1<w:
                    root[now][migi]=-1
                if 0<i:
                    root[now][ue]=-1
    #print(root)
    max=0
    
    for start in range(hw):
        if ina[start]==-1:
           # print(start,"is unreachable")
            continue
        dist=[0]*(hw)
        now=start
        dist[start]=0
        visted=[0]*(hw)
        toVis=deque()
        tv_append=toVis.append
        visted[now]=1
        for i in range(hw):
            if root[now][i]!=-1:
                tv_append(i)
                dist[i]=dist[now]+1
        while len(toVis)>0:
            now=toVis.popleft()
            visted[now]=1
            le=dist[now]
            for i in range(hw):
                if root[now][i]!=-1 and visted[i]!=1:
                    tv_append(i)
                    dist[i]=le+1
        farest=dist[now]
        if max<farest:
            max=farest
    print(max)
            
if __name__=="__main__":
    main()


    

Fixed submission:
h,w=map(int,input().split())
n=h*w
inf=10**6
field=[]
for i in range(h):
    field.append(input())
dist=[[inf]*n for i in range(n)]
for i in range(h):
    for j in range(w):
        if field[i][j]=="#":continue
        if j+1<w and field[i][j+1]!="#":
            dist[i*w+j][i*w+j+1]=1
            dist[i*w+j+1][i*w+j]=1
        if i+1<h and field[i+1][j]!="#":
            dist[i*w+j][(i+1)*w+j]=1
            dist[(i+1)*w+j][i*w+j]=1
for i in range(n):
    for j in range(n):
        for k in range(n):
            dist[j][k]=min(dist[j][k],dist[j][i]+dist[i][k])
ans=0
for i in range(n):
    for j in range(n):
        if i==j:
            continue
        if dist[i][j]==inf:
            continue
        ans=max(ans,dist[i][j])
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
def main():
    h,w=map(int,input().split())
    maze=[]
    r_append=maze.append
    for i in range(h):
        #r_append=maze.append
        #row=input()
        r_append(input())
    #print(maze)
    #root=[[-1 for i in range(h*w)] for i in range(h*w)]
    root=[0]*(h*w)
    for i in range(h*w):
        root[i]=[-1]*(h*w)
    ina=[i for i in range(h*w)]
    for i in range(h):
        for j in range(w):
        # print(maze[i][j])
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if maze[i][j]==".":
                if j>0:
                    if maze[i][j-1]!="#":
                        root[now][hidari]=0
                if i+1<h:
                    if maze[i+1][j]!="#":
                        root[now][sita]=0
                if j+1<w:
                    if maze[i][j+1]!="#":
                        root[now][migi]=0
                if 0<i:
                    if maze[i-1][j]!="#":
                        root[now][ue]=0
            else:
                ina[now]=-1
                if j>0:
                    root[now][hidari]=-1
                if i+1<h:
                    root[now][sita]=-1
                if j+1<w:
                    root[now][migi]=-1
                if 0<i:
                    root[now][ue]=-1
    #print(root)
    max=0
    hw=h*w
    for start in range(hw):
        if ina[start]==-1:
           # print(start,"is unreachable")
            continue
        dist=[0]*(hw)
        now=start
        dist[start]=0
        visted=[0]*(hw)
        toVis=deque()
        tv_append=toVis.append
        visted[now]=1
        for i in range(hw):
            if root[now][i]!=-1:
                tv_append(i)
                dist[i]=dist[now]+1
        while len(toVis)>0:
            now=toVis.popleft()
            visted[now]=1
            le=dist[now]
            for i in range(hw):
                if root[now][i]!=-1 and visted[i]!=1:
                    tv_append(i)
                    dist[i]=le+1
        farest=dist[now]
        if max<farest:
            max=farest
    print(max)
            
if __name__=="__main__":
    main()

Fixed submission:
h,w=map(int,input().split())
n=h*w
inf=10**6
field=[]
for i in range(h):
    field.append(input())
dist=[[inf]*n for i in range(n)]
for i in range(h):
    for j in range(w):
        if field[i][j]=="#":continue
        if j+1<w and field[i][j+1]!="#":
            dist[i*w+j][i*w+j+1]=1
            dist[i*w+j+1][i*w+j]=1
        if i+1<h and field[i+1][j]!="#":
            dist[i*w+j][(i+1)*w+j]=1
            dist[(i+1)*w+j][i*w+j]=1
for i in range(n):
    for j in range(n):
        for k in range(n):
            dist[j][k]=min(dist[j][k],dist[j][i]+dist[i][k])
ans=0
for i in range(n):
    for j in range(n):
        if i==j:
            continue
        if dist[i][j]==inf:
            continue
        ans=max(ans,dist[i][j])
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
def main():
    h,w=map(int,input().split())
    maze=[]
    r_append=maze.append
    for i in range(h):
        #r_append=maze.append
        row=input()
        r_append(row)
    #print(maze)
    #root=[[-1 for i in range(h*w)] for i in range(h*w)]
    root=[0]*(h*w)
    for i in range(h*w):
        root[i]=[-1]*(h*w)
    ina=[i for i in range(h*w)]
    for i in range(h):
        for j in range(w):
        # print(maze[i][j])
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if maze[i][j]==".":
                if j>0:
                    if maze[i][j-1]!="#":
                        root[now][hidari]=0
                if i+1<h:
                    if maze[i+1][j]!="#":
                        root[now][sita]=0
                if j+1<w:
                    if maze[i][j+1]!="#":
                        root[now][migi]=0
                if 0<i:
                    if maze[i-1][j]!="#":
                        root[now][ue]=0
            else:
                ina[now]=-1
                if j>0:
                    root[now][hidari]=-1
                if i+1<h:
                    root[now][sita]=-1
                if j+1<w:
                    root[now][migi]=-1
                if 0<i:
                    root[now][ue]=-1
    #print(root)
    max=0
    hw=h*w
    for start in range(hw):
        if ina[start]==-1:
           # print(start,"is unreachable")
            continue
        dist=[0]*(hw)
        now=start
        dist[start]=0
        visted=[0]*(hw)
        toVis=deque()
        tv_append=toVis.append
        visted[now]=1
        for i in range(hw):
            if root[now][i]!=-1:
                tv_append(i)
                dist[i]=dist[now]+1
        while len(toVis)>0:
            now=toVis.popleft()
            visted[now]=1
            le=dist[now]
            for i in range(hw):
                if root[now][i]!=-1 and visted[i]!=1:
                    tv_append(i)
                    dist[i]=le+1
        farest=dist[now]
        if max<farest:
            max=farest
    print(max)
            
if __name__=="__main__":
    main()


    
            


Fixed submission:
h,w=map(int,input().split())
n=h*w
inf=10**6
field=[]
for i in range(h):
    field.append(input())
dist=[[inf]*n for i in range(n)]
for i in range(h):
    for j in range(w):
        if field[i][j]=="#":continue
        if j+1<w and field[i][j+1]!="#":
            dist[i*w+j][i*w+j+1]=1
            dist[i*w+j+1][i*w+j]=1
        if i+1<h and field[i+1][j]!="#":
            dist[i*w+j][(i+1)*w+j]=1
            dist[(i+1)*w+j][i*w+j]=1
for i in range(n):
    for j in range(n):
        for k in range(n):
            dist[j][k]=min(dist[j][k],dist[j][i]+dist[i][k])
ans=0
for i in range(n):
    for j in range(n):
        if i==j:
            continue
        if dist[i][j]==inf:
            continue
        ans=max(ans,dist[i][j])
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
def main():
    h,w=map(int,input().split())
    maze=[]
    r_append=maze.append
    for i in range(h):
        #r_append=maze.append
        row=input()
        r_append(row)
    #print(maze)
    #root=[[-1 for i in range(h*w)] for i in range(h*w)]
    root=[0]*(h*w)
    for i in range(h*w):
        root[i]=[-1]*(h*w)
    ina=[i for i in range(h*w)]
    for i in range(h):
        for j in range(w):
        # print(maze[i][j])
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if maze[i][j]==".":
                if j>0:
                    if maze[i][j-1]!="#":
                        root[now][hidari]=0
                if i+1<h:
                    if maze[i+1][j]!="#":
                        root[now][sita]=0
                if j+1<w:
                    if maze[i][j+1]!="#":
                        root[now][migi]=0
                if 0<i:
                    if maze[i-1][j]!="#":
                        root[now][ue]=0
            else:
                ina[now]=-1
                if j>0:
                    root[now][hidari]=-1
                if i+1<h:
                    root[now][sita]=-1
                if j+1<w:
                    root[now][migi]=-1
                if 0<i:
                    root[now][ue]=-1
    #print(root)
    max=0
    hw=h*w
    for start in range(hw):
        if ina[start]==-1:
           # print(start,"is unreachable")
            continue
        dist=[0]*(hw)
        now=start
        dist[start]=0
        visted=[0]*(hw)
        toVis=deque()
        visted[now]=1
        for i in range(hw):
            if root[now][i]!=-1:
                toVis.append(i)
                dist[i]=dist[now]+1
        while len(toVis)>0:
            now=toVis.popleft()
            visted[now]=1
            le=dist[now]
            for i in range(hw):
                if root[now][i]!=-1 and visted[i]!=1:
                    toVis.append(i)
                    dist[i]=le+1
        farest=dist[now]
        if max<farest:
            max=farest
    print(max)
            
if __name__=="__main__":
    main()


    

Fixed submission:
h,w=map(int,input().split())
n=h*w
inf=10**6
field=[]
for i in range(h):
    field.append(input())
dist=[[inf]*n for i in range(n)]
for i in range(h):
    for j in range(w):
        if field[i][j]=="#":continue
        if j+1<w and field[i][j+1]!="#":
            dist[i*w+j][i*w+j+1]=1
            dist[i*w+j+1][i*w+j]=1
        if i+1<h and field[i+1][j]!="#":
            dist[i*w+j][(i+1)*w+j]=1
            dist[(i+1)*w+j][i*w+j]=1
for i in range(n):
    for j in range(n):
        for k in range(n):
            dist[j][k]=min(dist[j][k],dist[j][i]+dist[i][k])
ans=0
for i in range(n):
    for j in range(n):
        if i==j:
            continue
        if dist[i][j]==inf:
            continue
        ans=max(ans,dist[i][j])
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
def main():
    h,w=map(int,input().split())
    maze=[]
    r_append=maze.append
    for i in range(h):
        #r_append=maze.append
        row=input()
        r_append(row)
    #print(maze)
    #root=[[-1 for i in range(h*w)] for i in range(h*w)]
    root=[0]*(h*w)
    for i in range(h*w):
        root[i]=[-1]*(h*w)
    ina=[i for i in range(h*w)]
    for i in range(h):
        for j in range(w):
        # print(maze[i][j])
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if maze[i][j]==".":
                if j>0:
                    if maze[i][j-1]!="#":
                        root[now][hidari]=0
                if i+1<h:
                    if maze[i+1][j]!="#":
                        root[now][sita]=0
                if j+1<w:
                    if maze[i][j+1]!="#":
                        root[now][migi]=0
                if 0<i:
                    if maze[i-1][j]!="#":
                        root[now][ue]=0
            else:
                ina[now]=-1
                if j>0:
                    root[now][hidari]=-1
                if i+1<h:
                    root[now][sita]=-1
                if j+1<w:
                    root[now][migi]=-1
                if 0<i:
                    root[now][ue]=-1
    #print(root)
    max=0
    hw=h*w
    for start in range(hw):
        if ina[start]==-1:
           # print(start,"is unreachable")
            continue
        dist=[0]*(hw)
        now=start
        dist[start]=0
        visted=[0]*(hw)
        toVis=deque()
        visted[now]=1
        for i in range(hw):
            if root[now][i]!=-1:
                toVis.append(i)
                dist[i]=dist[now]+1
        while len(toVis)>0:
            now=toVis.popleft()
            visted[now]=1
            le=dist[now]
            for i in range(hw):
                if root[now][i]!=-1 and visted[i]!=1:
                    toVis.append(i)
                    dist[i]=le+1
        farest=dist[now]
        if max<farest:
            max=farest
    print(max)
            
if __name__=="__main__":
    main()


    

Fixed submission:
h,w=map(int,input().split())
n=h*w
inf=10**6
field=[]
for i in range(h):
    field.append(input())
dist=[[inf]*n for i in range(n)]
for i in range(h):
    for j in range(w):
        if field[i][j]=="#":continue
        if j+1<w and field[i][j+1]!="#":
            dist[i*w+j][i*w+j+1]=1
            dist[i*w+j+1][i*w+j]=1
        if i+1<h and field[i+1][j]!="#":
            dist[i*w+j][(i+1)*w+j]=1
            dist[(i+1)*w+j][i*w+j]=1
for i in range(n):
    for j in range(n):
        for k in range(n):
            dist[j][k]=min(dist[j][k],dist[j][i]+dist[i][k])
ans=0
for i in range(n):
    for j in range(n):
        if i==j:
            continue
        if dist[i][j]==inf:
            continue
        ans=max(ans,dist[i][j])
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
h,w=map(int,input().split())
n=h*w
inf=10**6
field=[]
for i in range(h):
    field.append(input())
dist=[[inf]*n for i in range(n)]
for i in range(h):
    for j in range(w):
        if field[i][j]=="#":continue
        if j+1<w and field[i][j+1]!="#":
            dist[i*w+j][i*w+j+1]=1
            dist[i*w+j+1][i*w+j]=1
        if i+1<h and field[i+1][j]!="#":
            dist[i*w+j][(i+1)*w+j]=1
            dist[(i+1)*w+j][i*w+j]=1
for i in range(n):
    for j in range(n):
        for k in range(n):
            dist[j][k]=min(dist[j][k],dist[j][i]+dist[i][k])
ans=0
for i in range(n):
    for j in range(n):
        if i==j:
            continue
        if dist[i][j]==inf:
            continue
        ans=max(ans,dist[i][j])
print(ans)

Fixed submission:
h,w=map(int,input().split())
n=h*w
inf=10**6
field=[]
for i in range(h):
    field.append(input())
dist=[[inf]*n for i in range(n)]
for i in range(h):
    for j in range(w):
        if field[i][j]=="#":continue
        if j+1<w and field[i][j+1]!="#":
            dist[i*w+j][i*w+j+1]=1
            dist[i*w+j+1][i*w+j]=1
        if i+1<h and field[i+1][j]!="#":
            dist[i*w+j][(i+1)*w+j]=1
            dist[(i+1)*w+j][i*w+j]=1
for i in range(n):
    for j in range(n):
        for k in range(n):
            dist[j][k]=min(dist[j][k],dist[j][i]+dist[i][k])
ans=0
for i in range(n):
    for j in range(n):
        if i==j:
            continue
        if dist[i][j]==inf:
            continue
        ans=max(ans,dist[i][j])
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import queue
def main():
    h,w=map(int,input().split())
    maze=[]
    r_append=maze.append
    for i in range(h):
        #r_append=maze.append
        row=input()
        r_append(row)
    #print(maze)
    #root=[[-1 for i in range(h*w)] for i in range(h*w)]
    root=[0]*(h*w)
    for i in range(h*w):
        root[i]=[-1]*(h*w)
    ina=[i for i in range(h*w)]
    for i in range(h):
        for j in range(w):
        # print(maze[i][j])
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if maze[i][j]==".":
                if j>0:
                    if maze[i][j-1]!="#":
                        root[now][hidari]=0
                if i+1<h:
                    if maze[i+1][j]!="#":
                        root[now][sita]=0
                if j+1<w:
                    if maze[i][j+1]!="#":
                        root[now][migi]=0
                if 0<i:
                    if maze[i-1][j]!="#":
                        root[now][ue]=0
            else:
                ina[now]=-1
                if j>0:
                    root[now][hidari]=-1
                if i+1<h:
                    root[now][sita]=-1
                if j+1<w:
                    root[now][migi]=-1
                if 0<i:
                    root[now][ue]=-1
    #print(root)
    max=0
    hw=h*w
    for start in range(hw):
        if ina[start]==-1:
           # print(start,"is unreachable")
            continue
        dist=[0]*(hw)
        now=start
        dist[start]=0
        visted=[0]*(hw)
        toVis=queue.Queue()
        visted[now]=1
        for i in range(hw):
            if root[now][i]!=-1:
                toVis.put(i)
                dist[i]=dist[now]+1
        while toVis.empty()!=True:
            now=toVis.get()
            visted[now]=1
            le=dist[now]
            for i in range(hw):
                if root[now][i]!=-1 and visted[i]!=1:
                    toVis.put(i)
                    dist[i]=le+1
        farest=dist[now]
        if max<farest:
            max=farest
    print(max)
            
if __name__=="__main__":
    main()

Fixed submission:
h,w=map(int,input().split())
n=h*w
inf=10**6
field=[]
for i in range(h):
    field.append(input())
dist=[[inf]*n for i in range(n)]
for i in range(h):
    for j in range(w):
        if field[i][j]=="#":continue
        if j+1<w and field[i][j+1]!="#":
            dist[i*w+j][i*w+j+1]=1
            dist[i*w+j+1][i*w+j]=1
        if i+1<h and field[i+1][j]!="#":
            dist[i*w+j][(i+1)*w+j]=1
            dist[(i+1)*w+j][i*w+j]=1
for i in range(n):
    for j in range(n):
        for k in range(n):
            dist[j][k]=min(dist[j][k],dist[j][i]+dist[i][k])
ans=0
for i in range(n):
    for j in range(n):
        if i==j:
            continue
        if dist[i][j]==inf:
            continue
        ans=max(ans,dist[i][j])
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import queue
import numpy
def main():
    h,w=map(int,input().split())
    maze=[]
    r_append=maze.append
    for i in range(h):
        #r_append=maze.append
        row=input()
        r_append(row)
    #print(maze)
    root=numpy.array([[-1 for i in range(h*w)] for i in range(h*w)])
    ina=numpy.array([i for i in range(h*w)])
    for i in range(h):
        for j in range(w):
        # print(maze[i][j])
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if maze[i][j]==".":
                if j>0:
                    if maze[i][j-1]!="#":
                        root[now][hidari]=0
                if i+1<h:
                    if maze[i+1][j]!="#":
                        root[now][sita]=0
                if j+1<w:
                    if maze[i][j+1]!="#":
                        root[now][migi]=0
                if 0<i:
                    if maze[i-1][j]!="#":
                        root[now][ue]=0
            else:
                ina[now]=-1
                if j>0:
                    root[now][hidari]=-1
                if i+1<h:
                    root[now][sita]=-1
                if j+1<w:
                    root[now][migi]=-1
                if 0<i:
                    root[now][ue]=-1
    #print(root)
    max=0
    hw=h*w
    for start in range(hw):
        if ina[start]==-1:
           # print(start,"is unreachable")
            continue
        dist=[0]*(hw)
        now=start
        dist[start]=0
        visted=[0]*(hw)
        toVis=queue.Queue()
        visted[now]=1
        for i in range(hw):
            if root[now][i]!=-1:
                toVis.put(i)
                dist[i]=dist[now]+1
        while toVis.empty()!=True:
            now=toVis.get()
            visted[now]=1
            le=dist[now]
            for i in range(hw):
                if root[now][i]!=-1 and visted[i]!=1:
                    toVis.put(i)
                    dist[i]=le+1
        farest=dist[now]
        if max<farest:
            max=farest
    print(max)
            
if __name__=="__main__":
    main()


    
            

Fixed submission:
h,w=map(int,input().split())
n=h*w
inf=10**6
field=[]
for i in range(h):
    field.append(input())
dist=[[inf]*n for i in range(n)]
for i in range(h):
    for j in range(w):
        if field[i][j]=="#":continue
        if j+1<w and field[i][j+1]!="#":
            dist[i*w+j][i*w+j+1]=1
            dist[i*w+j+1][i*w+j]=1
        if i+1<h and field[i+1][j]!="#":
            dist[i*w+j][(i+1)*w+j]=1
            dist[(i+1)*w+j][i*w+j]=1
for i in range(n):
    for j in range(n):
        for k in range(n):
            dist[j][k]=min(dist[j][k],dist[j][i]+dist[i][k])
ans=0
for i in range(n):
    for j in range(n):
        if i==j:
            continue
        if dist[i][j]==inf:
            continue
        ans=max(ans,dist[i][j])
print(ans)

Buggy python submission (verdict: Runtime Error):
import queue
import numpy
def main():
    h,w=map(int,input().split())
    maze=[]
    r_append=maze.append
    for i in range(h):
        #r_append=maze.append
        row=input()
        r_append(row)
    #print(maze)
    root=numpy.array([[-1 for i in range(h*w)] for i in range(h*w)])
    ina=numpy.array([i for i in range(h*w)])
    for i in range(h):
        for j in range(w):
        # print(maze[i][j])
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if maze[i][j]==".":
                if j>0:
                    if maze[i][j-1]!="#":
                        root[now][hidari]=0
                if i+1<h:
                    if maze[i+1][j]!="#":
                        root[now][sita]=0
                if j+1<w:
                    if maze[i][j+1]!="#":
                        root[now][migi]=0
                if 0<i:
                    if maze[i-1][j]!="#":
                        root[now][ue]=0
            else:
                ina[now]=-1
                if j>0:
                    root[now][hidari]=-1
                if i+1<h:
                    root[now][sita]=-1
                if j+1<w:
                    root[now][migi]=-1
                if 0<i:
                    root[now][ue]=-1
    #print(root)
    max=0
    hw=h*w
    for start in range(hw):
        if ina[start]==-1:
           # print(start,"is unreachable")
            continue
        dist=[0]*(hw)
        now=start
        dist[start]=0
        visted=[0]*(hw)
        toVis=queue.Queue()
        visted[now]=1
        for i in range(hw):
            if root[now][i]!=-1:
                toVis.put(i)
                dist[i]=dist[now]+1
        while toVis.empty()!=True:
            now=toVis.get()
            visted[now]=1
            le=dist[now]
            for i in range(hw):
                if root[now][i]!=-1 and visted[i]!=1:
                    toVis.put(i)
                    dist[i]=le+1
        farest=dist[now]
        if max<farest:
            max=farest
    print(max)
            
if __name__=="__main__":
    main()


    
            

Fixed submission:
h,w=map(int,input().split())
n=h*w
inf=10**6
field=[]
for i in range(h):
    field.append(input())
dist=[[inf]*n for i in range(n)]
for i in range(h):
    for j in range(w):
        if field[i][j]=="#":continue
        if j+1<w and field[i][j+1]!="#":
            dist[i*w+j][i*w+j+1]=1
            dist[i*w+j+1][i*w+j]=1
        if i+1<h and field[i+1][j]!="#":
            dist[i*w+j][(i+1)*w+j]=1
            dist[(i+1)*w+j][i*w+j]=1
for i in range(n):
    for j in range(n):
        for k in range(n):
            dist[j][k]=min(dist[j][k],dist[j][i]+dist[i][k])
ans=0
for i in range(n):
    for j in range(n):
        if i==j:
            continue
        if dist[i][j]==inf:
            continue
        ans=max(ans,dist[i][j])
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import queue
def main():
    h,w=map(int,input().split())
    maze=[]
    r_append=maze.append
    for i in range(h):
        #r_append=maze.append
        row=input()
        r_append(row)
    #print(maze)
    root=[[-1 for i in range(h*w)] for i in range(h*w)]
    ina=[i for i in range(h*w)]
    for i in range(h):
        for j in range(w):
        # print(maze[i][j])
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if maze[i][j]==".":
                if j>0:
                    if maze[i][j-1]!="#":
                        root[now][hidari]=0
                if i+1<h:
                    if maze[i+1][j]!="#":
                        root[now][sita]=0
                if j+1<w:
                    if maze[i][j+1]!="#":
                        root[now][migi]=0
                if 0<i:
                    if maze[i-1][j]!="#":
                        root[now][ue]=0
            else:
                ina[now]=-1
                if j>0:
                    root[now][hidari]=-1
                if i+1<h:
                    root[now][sita]=-1
                if j+1<w:
                    root[now][migi]=-1
                if 0<i:
                    root[now][ue]=-1
    #print(root)
    max=0
    hw=h*w
    for start in ina:
        dist=[0]*(hw)
        now=start
        dist[start]=0
        visted=[0]*(hw)
        toVis=queue.Queue()
        visted[now]=1
        for i in range(hw):
            if root[now][i]!=-1:
                toVis.put(i)
                dist[i]=dist[now]+1
        while toVis.empty()!=True:
            now=toVis.get()
            visted[now]=1
            le=dist[now]
            for i in range(hw):
                if root[now][i]!=-1 and visted[i]!=1:
                    toVis.put(i)
                    dist[i]=le+1
        farest=dist[now]
        if max<farest:
            max=farest
    print(max)
            
if __name__=="__main__":
    main()


    

Fixed submission:
h,w=map(int,input().split())
n=h*w
inf=10**6
field=[]
for i in range(h):
    field.append(input())
dist=[[inf]*n for i in range(n)]
for i in range(h):
    for j in range(w):
        if field[i][j]=="#":continue
        if j+1<w and field[i][j+1]!="#":
            dist[i*w+j][i*w+j+1]=1
            dist[i*w+j+1][i*w+j]=1
        if i+1<h and field[i+1][j]!="#":
            dist[i*w+j][(i+1)*w+j]=1
            dist[(i+1)*w+j][i*w+j]=1
for i in range(n):
    for j in range(n):
        for k in range(n):
            dist[j][k]=min(dist[j][k],dist[j][i]+dist[i][k])
ans=0
for i in range(n):
    for j in range(n):
        if i==j:
            continue
        if dist[i][j]==inf:
            continue
        ans=max(ans,dist[i][j])
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import queue
def main():
    h,w=map(int,input().split())
    maze=[]
    r_append=maze.append
    for i in range(h):
        #r_append=maze.append
        row=input()
        r_append(row)
    #print(maze)
    root=[[-1 for i in range(h*w)] for i in range(h*w)]
    ina=[0]*(h*w)
    for i in range(h):
        for j in range(w):
        # print(maze[i][j])
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if maze[i][j]==".":
                if j>0:
                    if maze[i][j-1]!="#":
                        root[now][hidari]=0
                if i+1<h:
                    if maze[i+1][j]!="#":
                        root[now][sita]=0
                if j+1<w:
                    if maze[i][j+1]!="#":
                        root[now][migi]=0
                if 0<i:
                    if maze[i-1][j]!="#":
                        root[now][ue]=0
            else:
                ina[now]=-1
                if j>0:
                    root[now][hidari]=-1
                if i+1<h:
                    root[now][sita]=-1
                if j+1<w:
                    root[now][migi]=-1
                if 0<i:
                    root[now][ue]=-1
    #print(root)
    max=0
    hw=h*w
    for start in range(hw):
        if ina[start]==-1:
           # print(start,"is unreachable")
            continue
        dist=[0]*(hw)
        now=start
        dist[start]=0
        visted=[0]*(hw)
        toVis=queue.Queue()
        visted[now]=1
        for i in range(hw):
            if root[now][i]!=-1:
                toVis.put(i)
                dist[i]=dist[now]+1
        while toVis.empty()!=True:
            now=toVis.get()
            visted[now]=1
            le=dist[now]
            for i in range(hw):
                if root[now][i]!=-1 and visted[i]!=1:
                    toVis.put(i)
                    dist[i]=le+1
        farest=dist[now]
        if max<farest:
            max=farest
    print(max)
            
if __name__=="__main__":
    main()


Fixed submission:
h,w=map(int,input().split())
n=h*w
inf=10**6
field=[]
for i in range(h):
    field.append(input())
dist=[[inf]*n for i in range(n)]
for i in range(h):
    for j in range(w):
        if field[i][j]=="#":continue
        if j+1<w and field[i][j+1]!="#":
            dist[i*w+j][i*w+j+1]=1
            dist[i*w+j+1][i*w+j]=1
        if i+1<h and field[i+1][j]!="#":
            dist[i*w+j][(i+1)*w+j]=1
            dist[(i+1)*w+j][i*w+j]=1
for i in range(n):
    for j in range(n):
        for k in range(n):
            dist[j][k]=min(dist[j][k],dist[j][i]+dist[i][k])
ans=0
for i in range(n):
    for j in range(n):
        if i==j:
            continue
        if dist[i][j]==inf:
            continue
        ans=max(ans,dist[i][j])
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import queue
def main():
    h,w=map(int,input().split())
    maze=[]
    r_append=maze.append
    for i in range(h):
        #r_append=maze.append
        row=input()
        r_append(row)
    #print(maze)
    root=[[-1 for i in range(h*w)] for i in range(h*w)]
    for i in range(h):
        for j in range(w):
        # print(maze[i][j])
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if maze[i][j]==".":
                if j>0:
                    if maze[i][j-1]!="#":
                        root[now][hidari]=0
                if i+1<h:
                    if maze[i+1][j]!="#":
                        root[now][sita]=0
                if j+1<w:
                    if maze[i][j+1]!="#":
                        root[now][migi]=0
                if 0<i:
                    if maze[i-1][j]!="#":
                        root[now][ue]=0
            else:
                if j>0:
                    root[now][hidari]=-1
                if i+1<h:
                    root[now][sita]=-1
                if j+1<w:
                    root[now][migi]=-1
                if 0<i:
                    root[now][ue]=-1
    max=0
    hw=h*w
    for start in range(hw):
        dist=[-1]*(hw)
        now=start
        dist[start]=0
        visted=[0]*(hw)
        toVis=queue.Queue()
        visted[now]=1
        for i in range(hw):
            if root[now][i]!=-1:
                toVis.put(i)
                dist[i]=dist[now]+1
        while toVis.empty()!=True:
            now=toVis.get()
            visted[now]=1
            le=dist[now]
            for i in range(hw):
                if root[now][i]!=-1 and visted[i]!=1:
                    toVis.put(i)
                    dist[i]=le+1
        #print("s:",start,"g:",goal,"len",dist[goal])
        farest=dist[now]
        if max<farest:
            max=farest
    print(max)
            
if __name__=="__main__":
    main()


    

Fixed submission:
h,w=map(int,input().split())
n=h*w
inf=10**6
field=[]
for i in range(h):
    field.append(input())
dist=[[inf]*n for i in range(n)]
for i in range(h):
    for j in range(w):
        if field[i][j]=="#":continue
        if j+1<w and field[i][j+1]!="#":
            dist[i*w+j][i*w+j+1]=1
            dist[i*w+j+1][i*w+j]=1
        if i+1<h and field[i+1][j]!="#":
            dist[i*w+j][(i+1)*w+j]=1
            dist[(i+1)*w+j][i*w+j]=1
for i in range(n):
    for j in range(n):
        for k in range(n):
            dist[j][k]=min(dist[j][k],dist[j][i]+dist[i][k])
ans=0
for i in range(n):
    for j in range(n):
        if i==j:
            continue
        if dist[i][j]==inf:
            continue
        ans=max(ans,dist[i][j])
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import queue
def main():
    h,w=map(int,input().split())
    maze=[]
    for i in range(h):
        row=input()
        maze.append(row)
    #print(maze)
    root=[[-1 for i in range(h*w)] for i in range(h*w)]
    for i in range(h):
        for j in range(w):
        # print(maze[i][j])
            if maze[i][j]==".":
                now=w*i+j
                hidari=w*i+j-1
                migi=w*i+j+1
                ue=w*(i-1)+j
                sita=w*(i+1)+j
                if j>0:
                    if maze[i][j-1]!="#":
                        root[now][hidari]=0
                if i+1<h:
                    if maze[i+1][j]!="#":
                        root[now][sita]=0
                if j+1<w:
                    if maze[i][j+1]!="#":
                        root[now][migi]=0
                if 0<i:
                    if maze[i-1][j]!="#":
                        root[now][ue]=0
            else:
                now=w*i+j
                now=w*i+j
                hidari=w*i+j-1
                migi=w*i+j+1
                ue=w*(i-1)+j
                sita=w*(i+1)+j
                if j>0:
                    root[now][hidari]=-1
                if i+1<h:
                    root[now][sita]=-1
                if j+1<w:
                    root[now][migi]=-1
                if 0<i:
                    root[now][ue]=-1
    #print(root)
    max=0
    for start in range(h*w):
        dist=[-1]*(h*w)
        now=start
        dist[start]=0
        visted=[0]*(h*w)
        toVis=queue.Queue()
        visted[now]=1
        for i in range(h*w):
            if root[now][i]!=-1:
                toVis.put(i)
                dist[i]=dist[now]+1
        while toVis.empty()!=True:
            now=toVis.get()
            visted[now]=1
            for i in range(h*w):
                if root[now][i]!=-1 and visted[i]!=1:
                    toVis.put(i)
                    dist[i]=dist[now]+1
        #print("s:",start,"g:",goal,"len",dist[goal])
        farest=dist[now]
        if max<farest:
            max=farest
    print(max)
            
if __name__=="__main__":
    main()


    

Fixed submission:
h,w=map(int,input().split())
n=h*w
inf=10**6
field=[]
for i in range(h):
    field.append(input())
dist=[[inf]*n for i in range(n)]
for i in range(h):
    for j in range(w):
        if field[i][j]=="#":continue
        if j+1<w and field[i][j+1]!="#":
            dist[i*w+j][i*w+j+1]=1
            dist[i*w+j+1][i*w+j]=1
        if i+1<h and field[i+1][j]!="#":
            dist[i*w+j][(i+1)*w+j]=1
            dist[(i+1)*w+j][i*w+j]=1
for i in range(n):
    for j in range(n):
        for k in range(n):
            dist[j][k]=min(dist[j][k],dist[j][i]+dist[i][k])
ans=0
for i in range(n):
    for j in range(n):
        if i==j:
            continue
        if dist[i][j]==inf:
            continue
        ans=max(ans,dist[i][j])
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import queue
h,w=map(int,input().split())
maze=[]
def func(n):
    if n=="#":
        return -1
    else:
        return 0


for i in range(h):
    row=input()
    maze.append(row)
#print(maze)
root=[[-1 for i in range(h*w)] for i in range(h*w)]
for i in range(h):
    for j in range(w):
       # print(maze[i][j])
        if maze[i][j]==".":
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if j>0:
                if maze[i][j-1]!="#":
                    root[now][hidari]=0
            if i+1<h:
                if maze[i+1][j]!="#":
                    root[now][sita]=0
            if j+1<w:
                if maze[i][j+1]!="#":
                    root[now][migi]=0
            if 0<i:
                if maze[i-1][j]!="#":
                    root[now][ue]=0
        else:
            now=w*i+j
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if j>0:
                root[now][hidari]=-1
            if i+1<h:
                root[now][sita]=-1
            if j+1<w:
                root[now][migi]=-1
            if 0<i:
                root[now][ue]=-1
#print(root)
max=0
for start in range(h*w):
    dist=[-1]*(h*w)
    now=start
    dist[start]=0
    visted=[0]*(h*w)
    toVis=queue.Queue()
    visted[now]=1
    for i in range(h*w):
        if root[now][i]!=-1:
            toVis.put(i)
            dist[i]=dist[now]+1
    while toVis.empty()!=True:
        now=toVis.get()
        visted[now]=1
        for i in range(h*w):
            if root[now][i]!=-1 and visted[i]!=1:
                toVis.put(i)
                dist[i]=dist[now]+1
    #print("s:",start,"g:",goal,"len",dist[goal])
    farest=dist[now]
    if max<farest:
        max=farest
print(max)
        

Fixed submission:
h,w=map(int,input().split())
n=h*w
inf=10**6
field=[]
for i in range(h):
    field.append(input())
dist=[[inf]*n for i in range(n)]
for i in range(h):
    for j in range(w):
        if field[i][j]=="#":continue
        if j+1<w and field[i][j+1]!="#":
            dist[i*w+j][i*w+j+1]=1
            dist[i*w+j+1][i*w+j]=1
        if i+1<h and field[i+1][j]!="#":
            dist[i*w+j][(i+1)*w+j]=1
            dist[(i+1)*w+j][i*w+j]=1
for i in range(n):
    for j in range(n):
        for k in range(n):
            dist[j][k]=min(dist[j][k],dist[j][i]+dist[i][k])
ans=0
for i in range(n):
    for j in range(n):
        if i==j:
            continue
        if dist[i][j]==inf:
            continue
        ans=max(ans,dist[i][j])
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import queue
h,w=map(int,input().split())
maze=[]
def func(n):
    if n=="#":
        return -1
    else:
        return 0


for i in range(h):
    row=input()
    maze.append(row)
#print(maze)
root=[[-1 for i in range(h*w)] for i in range(h*w)]
for i in range(h):
    for j in range(w):
       # print(maze[i][j])
        if maze[i][j]==".":
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if j>0:
                if maze[i][j-1]!="#":
                    root[now][hidari]=0
            if i+1<h:
                if maze[i+1][j]!="#":
                    root[now][sita]=0
            if j+1<w:
                if maze[i][j+1]!="#":
                    root[now][migi]=0
            if 0<i:
                if maze[i-1][j]!="#":
                    root[now][ue]=0
        else:
            now=w*i+j
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if j>0:
                root[now][hidari]=-1
            if i+1<h:
                root[now][sita]=-1
            if j+1<w:
                root[now][migi]=-1
            if 0<i:
                root[now][ue]=-1
#print(root)
max=0
for start in range(h*w):
    dist=[-1]*(h*w)
    now=start
    dist[start]=0
    visted=[0]*(h*w)
    toVis=queue.Queue()
    visted[now]=1
    for i in range(h*w):
        if root[now][i]!=-1:
            toVis.put(i)
            dist[i]=dist[now]+1
    while toVis.empty()!=True:
        now=toVis.get()
        visted[now]=1
        for i in range(h*w):
            if root[now][i]!=-1 and visted[i]!=1:
                toVis.put(i)
                dist[i]=dist[now]+1
    #print("s:",start,"g:",goal,"len",dist[goal])
    farest=dist[now]
    if max<farest:
        max=farest
print(max)
        

Fixed submission:
h,w=map(int,input().split())
n=h*w
inf=10**6
field=[]
for i in range(h):
    field.append(input())
dist=[[inf]*n for i in range(n)]
for i in range(h):
    for j in range(w):
        if field[i][j]=="#":continue
        if j+1<w and field[i][j+1]!="#":
            dist[i*w+j][i*w+j+1]=1
            dist[i*w+j+1][i*w+j]=1
        if i+1<h and field[i+1][j]!="#":
            dist[i*w+j][(i+1)*w+j]=1
            dist[(i+1)*w+j][i*w+j]=1
for i in range(n):
    for j in range(n):
        for k in range(n):
            dist[j][k]=min(dist[j][k],dist[j][i]+dist[i][k])
ans=0
for i in range(n):
    for j in range(n):
        if i==j:
            continue
        if dist[i][j]==inf:
            continue
        ans=max(ans,dist[i][j])
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import queue
h,w=map(int,input().split())
maze=[]
def func(n):
    if n=="#":
        return -1
    else:
        return 0


for i in range(h):
    row=input()
    maze.append(row)
#print(maze)
root=[[-1 for i in range(h*w)] for i in range(h*w)]
for i in range(h):
    for j in range(w):
       # print(maze[i][j])
        if maze[i][j]==".":
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if j>0:
                if maze[i][j-1]!="#":
                    root[now][hidari]=0
            if i+1<h:
                if maze[i+1][j]!="#":
                    root[now][sita]=0
            if j+1<w:
                if maze[i][j+1]!="#":
                    root[now][migi]=0
            if 0<i:
                if maze[i-1][j]!="#":
                    root[now][ue]=0
        else:
            now=w*i+j
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if j>0:
                root[now][hidari]=-1
            if i+1<h:
                root[now][sita]=-1
            if j+1<w:
                root[now][migi]=-1
            if 0<i:
                root[now][ue]=-1
#print(root)
max=0
for start in range(h*w):
    dist=[-1]*(h*w)
    now=start
    dist[start]=0
    visted=[0]*(h*w)
    toVis=queue.Queue()
    visted[now]=1
    for i in range(h*w):
        if root[now][i]!=-1:
            toVis.put(i)
            dist[i]=dist[now]+1
    while toVis.empty()!=True:
        now=toVis.get()
        visted[now]=1
        for i in range(h*w):
            if root[now][i]!=-1 and visted[i]!=1:
                toVis.put(i)
                dist[i]=dist[now]+1
    #print("s:",start,"g:",goal,"len",dist[goal])
    farest=dist[now]
    if max<farest:
        max=farest
print(max)
        

Fixed submission:
h,w=map(int,input().split())
n=h*w
inf=10**6
field=[]
for i in range(h):
    field.append(input())
dist=[[inf]*n for i in range(n)]
for i in range(h):
    for j in range(w):
        if field[i][j]=="#":continue
        if j+1<w and field[i][j+1]!="#":
            dist[i*w+j][i*w+j+1]=1
            dist[i*w+j+1][i*w+j]=1
        if i+1<h and field[i+1][j]!="#":
            dist[i*w+j][(i+1)*w+j]=1
            dist[(i+1)*w+j][i*w+j]=1
for i in range(n):
    for j in range(n):
        for k in range(n):
            dist[j][k]=min(dist[j][k],dist[j][i]+dist[i][k])
ans=0
for i in range(n):
    for j in range(n):
        if i==j:
            continue
        if dist[i][j]==inf:
            continue
        ans=max(ans,dist[i][j])
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import queue
h,w=map(int,input().split())
maze=[]
def func(n):
    if n=="#":
        return -1
    else:
        return 0


for i in range(h):
    row=input()
    maze.append(row)
#print(maze)
root=[[-1 for i in range(h*w)] for i in range(h*w)]
for i in range(h):
    for j in range(w):
       # print(maze[i][j])
        if maze[i][j]==".":
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if j>0:
                if maze[i][j-1]!="#":
                    root[now][hidari]=0
            if i+1<h:
                if maze[i+1][j]!="#":
                    root[now][sita]=0
            if j+1<w:
                if maze[i][j+1]!="#":
                    root[now][migi]=0
            if 0<i:
                if maze[i-1][j]!="#":
                    root[now][ue]=0
        else:
            now=w*i+j
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if j>0:
                root[now][hidari]=-1
            if i+1<h:
                root[now][sita]=-1
            if j+1<w:
                root[now][migi]=-1
            if 0<i:
                root[now][ue]=-1
#print(root)
max=0
for start in range(h*w):
    for goal in range(h*w):
        
        if start==goal:
            continue
        dist=[-1]*(h*w)
        now=start
        dist[start]=0
        visted=[0]*(h*w)
        toVis=queue.Queue()
        visted[now]=1
        for i in range(h*w):
            if root[now][i]!=-1:
                toVis.put(i)
                dist[i]=dist[now]+1
        while toVis.empty()!=True and now!=goal:
            now=toVis.get()
            
            visted[now]=1
            for i in range(h*w):
                if root[now][i]!=-1 and visted[i]!=1:
                    toVis.put(i)
                    dist[i]=dist[now]+1
        #print("s:",start,"g:",goal,"len",dist[goal])
        if max<dist[goal]:
            max=dist[goal]
print(max)
        




Fixed submission:
h,w=map(int,input().split())
n=h*w
inf=10**6
field=[]
for i in range(h):
    field.append(input())
dist=[[inf]*n for i in range(n)]
for i in range(h):
    for j in range(w):
        if field[i][j]=="#":continue
        if j+1<w and field[i][j+1]!="#":
            dist[i*w+j][i*w+j+1]=1
            dist[i*w+j+1][i*w+j]=1
        if i+1<h and field[i+1][j]!="#":
            dist[i*w+j][(i+1)*w+j]=1
            dist[(i+1)*w+j][i*w+j]=1
for i in range(n):
    for j in range(n):
        for k in range(n):
            dist[j][k]=min(dist[j][k],dist[j][i]+dist[i][k])
ans=0
for i in range(n):
    for j in range(n):
        if i==j:
            continue
        if dist[i][j]==inf:
            continue
        ans=max(ans,dist[i][j])
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import queue
h,w=map(int,input().split())
maze=[]
def func(n):
    if n=="#":
        return -1
    else:
        return 0


for i in range(h):
    row=input()
    maze.append(row)
#print(maze)
root=[[-1 for i in range(h*w)] for i in range(h*w)]
for i in range(h):
    for j in range(w):
       # print(maze[i][j])
        if maze[i][j]==".":
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if j>0:
                if maze[i][j-1]!="#":
                    root[now][hidari]=0
            if i+1<h:
                if maze[i+1][j]!="#":
                    root[now][sita]=0
            if j+1<w:
                if maze[i][j+1]!="#":
                    root[now][migi]=0
            if 0<i:
                if maze[i-1][j]!="#":
                    root[now][ue]=0
        else:
            now=w*i+j
            now=w*i+j
            hidari=w*i+j-1
            migi=w*i+j+1
            ue=w*(i-1)+j
            sita=w*(i+1)+j
            if j>0:
                root[now][hidari]=-1
            if i+1<h:
                root[now][sita]=-1
            if j+1<w:
                root[now][migi]=-1
            if 0<i:
                root[now][ue]=-1
#print(root)
max=0
for start in range(h*w):
    for goal in range(h*w):
        
        if start==goal:
            continue
        dist=[-1]*(h*w)
        now=start
        dist[start]=0
        visted=[0]*(h*w)
        toVis=queue.Queue()
        visted[now]=1
        for i in range(h*w):
            if root[now][i]!=-1:
                toVis.put(i)
                dist[i]=dist[now]+1
        while toVis.empty()!=True and now!=goal:
            now=toVis.get()
            
            visted[now]=1
            for i in range(h*w):
                if root[now][i]!=-1 and visted[i]!=1:
                    toVis.put(i)
                    dist[i]=dist[now]+1
        #print("s:",start,"g:",goal,"len",dist[goal])
        if max<dist[goal]:
            max=dist[goal]
print(max)
        




Fixed submission:
h,w=map(int,input().split())
n=h*w
inf=10**6
field=[]
for i in range(h):
    field.append(input())
dist=[[inf]*n for i in range(n)]
for i in range(h):
    for j in range(w):
        if field[i][j]=="#":continue
        if j+1<w and field[i][j+1]!="#":
            dist[i*w+j][i*w+j+1]=1
            dist[i*w+j+1][i*w+j]=1
        if i+1<h and field[i+1][j]!="#":
            dist[i*w+j][(i+1)*w+j]=1
            dist[(i+1)*w+j][i*w+j]=1
for i in range(n):
    for j in range(n):
        for k in range(n):
            dist[j][k]=min(dist[j][k],dist[j][i]+dist[i][k])
ans=0
for i in range(n):
    for j in range(n):
        if i==j:
            continue
        if dist[i][j]==inf:
            continue
        ans=max(ans,dist[i][j])
print(ans)