x, y = input().split()
grid = []






smallest = 1001
for i in range(int(y)):
    temp = input()
    temparr = temp.split()
    for c in range(len(temparr)):
        d = int(temparr[c])
        temparr[c] = d
    grid.append(temparr)
    if int(x) % 2 == 1 or int(y) % 2 == 1:
        continue
    if i % 2 == 0:
        for b in range(1, int(x), 2):
            if temparr[b] < smallest:
                smallest = temparr[b]
    elif i % 2 == 1:
        for b in range(0, int(x), 2):
            if temparr[b] < smallest:
                smallest = temparr[b]


big = 0
for i in range(int(y)):
    big+=sum(grid[i])
if int(x) % 2 == 1 or int(y) % 2 == 1:
    print(big)
else:
    print(big - smallest)