Problem:
Score : 500 points

Problem Statement

Given is a connected undirected graph with N vertices and M edges. The vertices are numbered 1 to N, and the edges are described by a grid of characters S.
If S_{i,j} is 1, there is an edge connecting Vertex i and j; otherwise, there is no such edge.

Determine whether it is possible to divide the vertices into non-empty sets V_1, \dots, V_k such that the following condition is satisfied. If the answer is yes, find the maximum possible number of sets, k, in such a division.

Every edge connects two vertices belonging to two "adjacent" sets. More formally, for every edge (i,j), there exists 1\leq t\leq k-1 such that i\in V_t,j\in V_{t+1} or i\in V_{t+1},j\in V_t holds.

Constraints

2 \leq N \leq 200

S_{i,j} is 0 or 1.

S_{i,i} is 0.

S_{i,j}=S_{j,i}

The given graph is connected.

N is an integer.

Input

Input is given from Standard Input in the following format:

N
S_{1,1}...S_{1,N}
:
S_{N,1}...S_{N,N}

Output

If it is impossible to divide the vertices into sets so that the condition is satisfied, print -1.
Otherwise, print the maximum possible number of sets, k, in a division that satisfies the condition.

Sample Input 1

2
01
10

Sample Output 1

2

We can put Vertex 1 in V_1 and Vertex 2 in V_2.

Sample Input 2

3
011
101
110

Sample Output 2

-1

Sample Input 3

6
010110
101001
010100
101000
100000
010000

Sample Output 3

4

Solution in Ruby (2.3.3) (judge verdict: Wrong Answer)

N = gets.to_i
s = {}
(0..(N-1)).each do |ind|
    array=gets.chomp.split("").map(&:to_i)
    s[ind] = array.map.with_index { |e,i| e ==1 ? i : nil }.compact
end
ret = Array.new(N)
queue = [0]
even_odd = 0
while !queue.empty? do
    queue.each do |i|
        ret[i] = even_odd
        if !s[i].map {|ind| ret[ind] }.select {|e| e!=nil && e==even_odd }.empty?
            puts "-1"
            exit
        end
    end
    queue = queue.map {|e| s[e] }.flatten.uniq
    ret.each_with_index do |e,i|
        queue.delete(i) if e != nil
    end
    even_odd = (even_odd + 1) % 2
end
puts 2