n, m = map(int, input().split())
a = [sum(map(int, input().split())) for _ in range(n)]
b = [[-10 ** 31] * 2 for _ in range(n)]
mx = [-10 ** 31] * 2
for i in range(n):
    b[i][0] = a[i]
    if i:
        b[i][0] = max(b[i][0], mx[1] + a[i])
        b[i][1] = mx[0] - a[i]
    for j in range(2):
        mx[j] = max(b[i][j], mx[j])
print(max(mx))