N,M = map(int,input().split())
A = []
for _ in range(N):
    A.append(sum(list(map(int,input().split()))))
ans = 0
if N == 1:
    print(A[0])
    exit()
ac_1 = [A[0]]
for i in range(1,N):
    if i%2 == 0:
        ac_1.append(ac_1[-1]+A[i])
    else:
        ac_1.append(ac_1[-1]-A[i])
ac_2 = [A[1]]
for i in range(2,N):
    if i%2 != 0:
        ac_2.append(ac_2[-1]+A[i])
    else:
        ac_2.append(ac_2[-1]-A[i])
ac_1,ac_2 = [0]+ac_1,[0]+ac_2

for i in range(len(ac_1)):
    for j in range(i+1,len(ac_1)):
        ans = max(ans,ac_1[j]-ac_1[i])
for i in range(len(ac_2)):
    for j in range(i+1,len(ac_2)):
        ans = max(ans,ac_2[j]-ac_2[i])
print(ans)