import sys

def main():
    m, n = map(int, sys.stdin.readline().split(' '))
    a = [list(map(int, sys.stdin.readline().split(' '))) for _ in range(m)]

    assert 1 <= min(m, n) and 6 <= max(n, m) <= 1000
    for r in a:
        assert 1 <= min(r) and max(r) <= 1000

    b = [[0] * n for _ in range(m)]

    for i in range(m):
        for j in range(n):
            for di in range(-1, 2):
                for dj in range(-1, 2):
                    if 0 <= i + di < m and 0 <= j + dj < n:
                        b[i][j] += a[i + di][j + dj]
            b[i][j] += a[i][j]

    best = max(map(max, b))

    answer = 0

    for i in range(m):
        for j in range(n):
            if answer == best * 2:
                continue
            if b[i][j] == best:
                current = 0
                for ii in range(m):
                    for jj in range(n):
                        if abs(i - ii) > 2 or abs(j - jj) > 2:
                            current = max(current, b[i][j] + b[ii][jj])
                answer = max(answer, current)

    print('{}'.format(answer / 2))


if __name__ == '__main__':
    main()