N,M=map(int, input().split())
D=[]
for i in range(N):
  A=list(map(int, input().split()))
  D.append(sum(A))
E=[0]*(N+1)
F=[0]*(N+1)
for i in range(1,N+1):
  E[i]=max(E[i-1],F[i-1]+D[i-1])
  F[i]=max(F[i-1],E[i-1]-D[i-1])
print(E[-1])