import java.util.*; import java.io.*; import java.math.*;
public class Main{
	//Don't have to see. start------------------------------------------
	static class InputIterator{
		ArrayList<String> inputLine = new ArrayList<String>(1024);
		int index = 0; int max; String read;
		InputIterator(){
			BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
			try{
				while((read = br.readLine()) != null){
					inputLine.add(read);
				}
			}catch(IOException e){}
			max = inputLine.size();
		}
		boolean hasNext(){return (index < max);}
		String next(){
			if(hasNext()){
				return inputLine.get(index++);
			}else{
				throw new IndexOutOfBoundsException("There is no more input");
			}
		}
	}
	static HashMap<Integer, String> CONVSTR = new HashMap<Integer, String>();
	static InputIterator ii = new InputIterator();//This class cannot be used in reactive problem.
	static PrintWriter out = new PrintWriter(System.out);
	static void flush(){out.flush();}
	static void myout(Object t){out.println(t);}
	static void myerr(Object t){System.err.print("debug:");System.err.println(t);}
	static String next(){return ii.next();}
	static boolean hasNext(){return ii.hasNext();}
	static int nextInt(){return Integer.parseInt(next());}
	static long nextLong(){return Long.parseLong(next());}
	static double nextDouble(){return Double.parseDouble(next());}
	static ArrayList<String> nextStrArray(){return myconv(next(), 8);}
	static ArrayList<String> nextCharArray(){return myconv(next(), 0);}
	static ArrayList<Integer> nextIntArray(){
		ArrayList<String> input = nextStrArray(); ArrayList<Integer> ret = new ArrayList<Integer>(input.size());
		for(int i = 0; i < input.size(); i++){
			ret.add(Integer.parseInt(input.get(i)));
		}
		return ret;
	}
	static ArrayList<Long> nextLongArray(){
		ArrayList<String> input = nextStrArray(); ArrayList<Long> ret = new ArrayList<Long>(input.size());
		for(int i = 0; i < input.size(); i++){
			ret.add(Long.parseLong(input.get(i)));
		}
		return ret;
	}
	static String myconv(Object list, int no){//only join
		String joinString = CONVSTR.get(no);
		if(list instanceof String[]){
			return String.join(joinString, (String[])list);
		}else if(list instanceof ArrayList){
			return String.join(joinString, (ArrayList)list);
		}else{
			throw new ClassCastException("Don't join");
		}
	}
	static ArrayList<String> myconv(String str, int no){//only split
		String splitString = CONVSTR.get(no);
		return new ArrayList<String>(Arrays.asList(str.split(splitString)));
	}
	public static void main(String[] args){
		CONVSTR.put(8, " "); CONVSTR.put(9, "\n"); CONVSTR.put(0, "");
		solve();flush();
	}
	//Don't have to see. end------------------------------------------
  static int N;
  static Node[] list;
	static void solve(){//Here is the main function
      N = nextInt();
      list = new Node[N];
      for(int i = 0; i < N; i++){
        list[i] = new Node(i);
      }
      for(int i = 0; i < N; i++){
        ArrayList<String> tmp = nextCharArray();
        for(int j = 0; j < N; j++){
          if(i != j && tmp.get(j).equals("1")){
            list[i].child.add(j);
          }
        }
      }
      int maxDepth = -1;
      for(int i = 0; i < N; i++){
        maxDepth = Math.max(maxDepth, bfs(i));
      }
      for(int i = 0; i < N - 1; i++){
        for(int j = i + 1; j < N; j++){
          if(list[i].child.contains(j) && list[j].child.contains(i)){
            if(list[i].depth % 2 == list[j].depth % 2){
              myout(-1);
              return;
            }
          }
        }
      }
      myout(maxDepth);
	}
	//Method addition frame start

static class Node{
  int no;
  ArrayList<Integer> child = new ArrayList<Integer>();
  boolean access = false;
  int depth = 1;
  Node(int no){
    this.no = no;
  }
}

static int bfs(int s){
  for(int i = 0; i < N; i++){
    list[i].access = false;
    list[i].depth = 1;
  }
  ArrayDeque<Integer> queue = new ArrayDeque<Integer>();
  queue.add(s);
  list[s].access = true;
  int maxDepth = 0;
  while(queue.size() > 0){
    int now = queue.pollFirst();
    maxDepth = list[now].depth;
    ArrayList<Integer> child = list[now].child;
    for(int i = 0; i < child.size(); i++){
      if(!list[child.get(i)].access){
        list[child.get(i)].access = true;
        list[child.get(i)].depth = list[now].depth + 1;
        queue.addLast(child.get(i));
      }
    }
  }
  return maxDepth;
}
  
	//Method addition frame end
}


Measured memory_bytes: 40704