n,m = map(int,input().split())
b = [0]*n
for i in range(n):
    b[i] = sum(list(map(int,input().split())))

d = [[-float("Inf")]*2 for i in range(n+1)]
d[0][1] = 0 #d[奇数][偶数]
for i in range(n):
    d[i+1][0] = max(b[i]+d[i][1], d[i][0])
    d[i+1][1] = max(d[i][0]-b[i], d[i][1])
print(max(d[-1][:]))