05. Dots

def check_right(matrix, row, column):
    if column < columns - 1 and matrix[row][column + 1] == "." and not [row, column + 1] in visited_positions:
        return True


def check_left(matrix, row, column):
    if column > 0 and matrix[row][column - 1] == "." and [row, column - 1] not in visited_positions:
        return True


def check_up(matrix, row, column):
    if row > 0 and matrix[row - 1][column] == "." and [row - 1, column] not in visited_positions:
        return True


def check_down(matrix, row, column):
    if row < rows - 1 and matrix[row + 1][column] == "." and [row + 1, column] not in visited_positions:
        return True


rows = int(input())
matrix = [list(input().split()) for i in range(rows)]
columns = len(matrix[0])
largest_len_of_connected_dots = 0

for r in range(rows):
    for c in range(columns):
        if matrix[r][c] == ".":
            visited_positions = []
            row = r
            column = c
            connected_dots = 0
            while True:
                if matrix[row][column] == "-":
                    break
                elif check_right(matrix, row, column):
                    visited_positions.append([row, column])
                    column += 1
                elif check_left(matrix, row, column):
                    visited_positions.append([row, column])
                    column -= 1
                elif check_up(matrix, row, column):
                    visited_positions.append([row, column])
                    row -= 1
                elif check_down(matrix, row, column):
                    visited_positions.append([row, column])
                    row += 1
                else:
                    matrix[row][column] = "-"
                    visited_positions = []
                    connected_dots += 1
                    row = r
                    column = c
                    if connected_dots > largest_len_of_connected_dots:
                        largest_len_of_connected_dots = connected_dots

print(largest_len_of_connected_dots)