"""
name: Nicholas Tamassia

Honor Code and Acknowledgments:

        This work complies with the JMU Honor Code.

       Comments here on your code and submission.
"""


def explore_island(grid: list[list[int]], start: tuple[int, int]) -> int:
    num_rows: int = len(grid)
    num_cols: int = len(grid[0])
    size: int = 0

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

        if grid[y][x] == 0:
            return

        nonlocal size
        size += 1
        grid[y][x] = 0

        if y > 0:
            recurse((x, y - 1))
        if y < num_rows - 1:
            recurse((x, y + 1))
        if x > 0:
            recurse((x - 1, y))
        if x < num_cols - 1:
            recurse((x + 1, y))

    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())

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

    num_rows: int = n
    num_cols: int = len(land_grid[0])

    largest_island: int = -1

    for y in range(0, num_rows):
        for x in range(0, num_cols):
            if land_grid[y][x] == 0:
                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()