output_description: 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.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      S_{1,1}...S_{1,N}
      :
      S_{N,1}...S_{N,N}
attempt: s = str(input())
  k = int(input())
  
  
  if len(s) == 1:
      if k < 2:
          ans = 0
      else:
          ans = k // 2
  elif len(s) == 2:
      if s[0] == s[1]:
          ans = k
      else:
          ans = 0
  else:
      if k == 1:
          ans = 0
          bef = ""
          befchen = False
          trignum = 0
          for i in range(len(s)):
              now = s[i]
              if bef == now:
                  if befchen == False:
                      ans += 1
                      befchen = True
                      trignum = i
              if befchen == True:
                  if trignum == i - 1:
                      befchen = False
              bef = now
  
      elif k >= 2:
          ans = 0
          bef = ""
          befchen = False
          trignum = 0
          for i in range(len(s)):
              now = s[i]
              if bef == now:
                  if befchen == False:
                      # print(now)
                      ans += 1
                      befchen = True
                      trignum = i
              if befchen == True:
                  if trignum == i - 1:
                      befchen = False
              bef = now
  
          if s[0] == s[-1]:
              if befchen == False:
                  ans += 1
  
          ans *= k
  
          if s[0] == s[-1]:
              if befchen == False:
                  ans -= 1
  
  print(ans)
  
problem_description: 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.
samples: [{"input": "2\n    01\n    10", "output": "2\n    \n\nWe can put Vertex 1 in V_1 and Vertex 2 in V_2.\n\n* * *"}, {"input": "3\n    011\n    101\n    110", "output": "-1\n    \n\n* * *"}, {"input": "6\n    010110\n    101001\n    010100\n    101000\n    100000\n    010000", "output": "4"}]