N, M = list(map(int, input().split()))
s = 0
best_min = float("inf")
for i in range(N):
    line = list(map(int, input().split()))
    s += sum(line)
    if i == 0:
        line = line[1:]
    elif i == N - 1:
        line = line[:-1]
    if line:
        best_min = min(min(line), best_min)

if N % 2 or M % 2:
    print(s)
else:
    print(s - best_min)