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从给定起点（一定为’.’），按照给定的若干跳跃（可以跨过障碍，但不可以落在’x’上），到达任意一个’.'的最小步骤次数集合中，选择一个最大的！

while True:    try:        n , m = map(int,input().split())        matrix = []        for i in range(n):            te = list(map(str,input()))            matrix.append(te)        begin_x,begin_y = map(int,input().split())        direction_num = int(input())                direction = []        for i in range(direction_num):            direction.append(list(map(int,input().split())))        visited = set()        visited.add((begin_x,begin_y))        stack = [(begin_x,begin_y,0)]        re = -1        while stack:            (x,y,step) = stack.pop(0)            re = max(re,step)            for [dx,dy] in direction:                temp_x = x+dx                temp_y = y+dy                 if 0<= temp_x <= n-1 and 0<= temp_y <= m-1 and (temp_x,temp_y) not in visited and matrix[temp_x][temp_y] == '.':                    visited.add((temp_x,temp_y))                    stack.append((temp_x,temp_y,step+1))        count = 0        for i in range(n):            for j in range(m):                if matrix[i][j] == '.':                    count+=1        if len(visited) == count:            print(re)        else:            print(-1)            except:        break