def get_max(N, M, field):
    result = 0
    if N%2 == 1 or M%2 == 1:
        for i in range(N):
            for j in range(M):
                result = result + field[i][j]
    else:
        minimum = 99999999 # min(min(field))
        for i in range(N):
            for j in range(M):
                if field[i][j] < minimum and field[i][j] != field[0][0] and field[i][j] != field[N-1][M-1]:
                    minimum = field[i][j]
                result = result + field[i][j]
        result = result - minimum
    return result

if __name__ == '__main__':
    a = input().split()
    N = int(a[0])
    M = int(a[1])
    field = [[0 for _ in range(M)] for _ in range(N)]
    for i in range(N):
        b = input().split()
        for j in range(M):
            field[i][j] = int(b[j])
    print(get_max(N, M, field))