output_description: Print a $8 \times 8$ chess board by strings where a square with a queen is
  represented by 'Q' and an empty square is represented by '.'.
input_description: In the first line, an integer $k$ is given. In the following $k$ lines, each
  square where a queen is already placed is given by two integers $r$ and $c$.
  $r$ and $c$ respectively denotes the row number and the column number. The
  row/column numbers start with 0.
attempt: def try_set(v):
      def print_board():
          for r, c in preset:
              if queen_pos[r] != c:
                  return
          for pos in queen_pos:
              for c in range(8):
                  print("Q" if c == pos else ".", end="")
              print()
  
      for h in range(8):
          if all((horizontal[h], dip_positive[v + h], dip_negative[v - h + 7])):
              queen_pos[v] = h
              if v == 7:
                  print_board()
              else:
                  horizontal[h] = dip_positive[v + h] = dip_negative[v - h + 7] = False
                  try_set(v + 1)
                  horizontal[h] = dip_positive[v + h] = dip_negative[v - h + 7] = True
  
  
  n = int(input())
  queen_pos = [None] * 8
  preset = [[pre for pre in map(int, input().split())] for _ in range(n)]
  horizontal = [True] * 8
  dip_positive = [True] * 15
  dip_negative = [True] * 15
  try_set(0)
  
problem_description: 8 Queens Problem
  
  The goal of 8 Queens Problem is to put eight queens on a chess-board such that
  none of them threatens any of others. A queen threatens the squares in the
  same row, in the same column, or on the same diagonals as shown in the
  following figure.
  
  ![](https://judgeapi.u-aizu.ac.jp/resources/images/IMAGE2_ALDS1_13_A_8queens)  
  
  For a given chess board where $k$ queens are already placed, find the solution
  of the 8 queens problem.
samples: [{"input": "2\n    2 2\n    5 3", "output": "......Q.\n    Q.......\n    ..Q.....\n    .......Q\n    .....Q..\n    ...Q....\n    .Q......\n    ....Q..."}]