def inpf() a=gets.chomp.split(" ").map(&:to_f)end

def inps() a=gets.chomp.split(" ")end

def copy(a) Marshal.load(Marshal.dump(a)) end

def kaijo(n,r = 10**9+7)(n < 2)? 1 : (2..n).inject{|memo,u|memo=(memo*u)%r} end

def na(n,d=0) Array.new(n,d)end

def na2(n,m,d=0) Array.new(n){Array.new(m,d)}end

def na3(n,m,l,d=0) Array.new(n){Array.new(m){Array.new(l,d)}}end

def inp() a=gets.chomp.split(" ").map(&:to_i)end

def r_up(a, b) (a+b-1)/b end

def sum(a) a.inject(:+) end

def bfs(table,memo)
  que = [[rand(table.size),1]]
  ans = 0
  while que.size > 0
    i,t = que.shift
    next if(memo[i] != 0)
    ans = t
    memo[i] = t
    table[i].each do |d|
      if(memo[d] != 0 and memo[d] != (t -1))
        return -1
      end
      que.push([d,t+1])
    end
  end
  return ans
end

n = inp[0]
table = na2(n,0)
memo = na(n,0)
n.times do |i|
  s = inps[0]
  s.split("").map(&:to_i).each.with_index do |d,j|
    table[i].push(j) if(d == 1)
  end
end
t = Time.now
ans = -1
while Time.now - t < 1.9
  ans = [bfs(table,memo),ans].max
  memo = na(n,0)
end
p ans
