output_description: Print the letter that follows C in alphabetical order.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      C
attempt: from collections import deque
  from typing import List
  
  
  def main():
      h, w = map(int, input().split())
      g = [input() for _ in range(h)]
      print(mm(h, w, g))
  
  
  def mm(h: int, w: int, g: List[List[str]]) -> int:
      ret = 0
      for i in range(h):
          for j in range(w):
              if g[i][j] == "#":
                  continue
              cnt = 0
              q = deque([(i, j, cnt)])
              v = set()
              while q:
                  ii, jj, cnt = q.popleft()
                  v.add((ii, jj))
                  ret = max(ret, cnt)
                  # ↓
                  if ii < h - 1 and g[ii + 1][jj] == "." and (ii + 1, jj) not in v:
                      q.append((ii + 1, jj, cnt + 1))
                  # →
                  if jj < w - 1 and g[ii][jj + 1] == "." and (ii, jj + 1) not in v:
                      q.append((ii, jj + 1, cnt + 1))
                  # ↑
                  if ii > 0 and g[ii - 1][jj] == "." and (ii - 1, jj) not in v:
                      q.append((ii - 1, jj, cnt + 1))
                  # ←
                  if jj > 0 and g[ii][jj - 1] == "." and (ii, jj - 1) not in v:
                      q.append((ii, jj - 1, cnt + 1))
      return ret
  
  
  if __name__ == "__main__":
      main()
  
problem_description: Statement
  
  Given is a lowercase English letter C that is not `z`. Print the letter that
  follows C in alphabetical order.
samples: [{"input": "a", "output": "b\n    \n\n`a` is followed by `b`.\n\n* * *"}, {"input": "y", "output": "z\n    \n\n`y` is followed by `z`."}]