"""
name: Nicholas Tamassia

Honor Code and Acknowledgments:

        This work complies with the JMU Honor Code.

       Comments here on your code and submission.
"""

import numpy as np

type LandGrid = np.ndarray[tuple[int, int], np.dtype[np.bool]]


def explore_island(grid: LandGrid, start: tuple[int, int]) -> int:
    num_rows, num_cols = grid.shape
    size: int = 0

    def recurse(coord: tuple[int, int]):
        x, y = coord

        if not grid[y, x]:
            return

        nonlocal size
        size += 1
        grid[y, x] = False

        neighbors: list[tuple[int, int]] = []

        if y > 0:
            neighbors.append((x, y - 1))
        if y < num_rows - 1:
            neighbors.append((x, y + 1))
        if x > 0:
            neighbors.append((x - 1, y))
        if x < num_cols - 1:
            neighbors.append((x + 1, y))

        for neighbor in neighbors:
            recurse(neighbor)

    recurse(start)

    return size


# All modules for CS 412 must include a main method that allows it
# to imported and invoked from other python scripts
def main():
    n: int = int(input())

    raw_matrix: list[list[int]] = [list(map(int, input().split())) for _ in range(0, n)]

    land_grid: LandGrid = np.array(raw_matrix, dtype=bool)
    num_rows, num_cols = land_grid.shape

    largest_island: int = -1

    for y in range(0, num_rows):
        for x in range(0, num_cols):
            if not land_grid[y, x]:
                continue

            island_size: int = explore_island(land_grid, (x, y))

            if island_size > largest_island:
                largest_island = island_size

    print(largest_island)


if __name__ == "__main__":
    main()