from collections import deque

H,W=map(int,input().split())

def f(x,y):
    return y*(W+2)+x

def g(n):
    return (n%(W+2),n//(W+2))

def BFS(V,A):
    Q=deque([V[0]])
    S={v:False for v in V}
    S[V[0]]=True
    T=[V[0]]

    while Q:
        v=Q.popleft()

        N=[]
        (x,y)=g(v)
        if A[y][x+1]==1 and not S[v+1]:
            Q.append(v+1)
            T.append(v+1)
            S[v+1]=True
            
        if A[y][x-1]==1 and not S[v-1]:
            Q.append(v-1)
            T.append(v-1)
            S[v-1]=True
            
        if A[y+1][x]==1 and not S[v+(W+2)]:
            Q.append(v+(W+2))
            T.append(v+(W+2))
            S[v+(W+2)]=True
            
        if A[y-1][x]==1 and not S[v-(W+2)]:
            Q.append(v-(W+2))
            T.append(v-(W+2))
            S[v-(W+2)]=True

    return T

A=[[0]*(W+2)]
for i in range(H):
    A.append([0]+list(map(int,input().split()))+[0])
A+=[[0]*(W+2)]

V=[]
for y in range(H+2):
    for x in range(W+2):
        if A[y][x]==1:
            V.append(f(x,y))

U=set()
X=set(V)
k=0
while U!=X:
    k+=1
    U|=set(BFS(list(X-U),A))

print(k)