미로탈출 - 파이썬

#미로탈출 
from collections import deque
def BFS(graph, a,b,cnt):
  dx=[0,1,0,-1]
  dy=[1,0,-1,0]
  queue=deque()
  queue.append((a,b))
  graph[a][b]=1
  while queue:
    x,y=queue.popleft()
    for i in range(4):
      nx=x+dx[i]
      ny=y+dy[i]
      if(nx>=0 and ny>=0 and nx<n and ny<m):
        if graph[nx][ny]==1:
          graph[nx][ny]=graph[x][y]+1
          queue.append((nx,ny))

n,m=map(int, input().split())
graph=[]
for i in range(n):
  graph.append(list(map(int, input())))
BFS(graph,0,0,1)
print(graph[n-1][m-1])