N,M = map(int,input().split())
A = []
for _ in range(N):
    A.append(sum(list(map(int,input().split()))))
A.reverse()
count,ans = 0,0
for i in range(N):
    if i%2 == 0:
        count += A[i]
    else:
        count -= A[i]
    ans = max(ans,count)
count = 0
for i in range(1,N):
    if i%2 != 0:
        count += A[i]
    else:
        count -= A[i]
    ans = max(ans,count)
print(ans)