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

print(max(dp[N]))