N,M=map(int,input().split())
A=[0]*N
for i in range(N):
    A[i]=sum(list(map(int,input().split())))
DP=[[0 for _ in range(4)] for _ in range(N+1)]
for i in range(N):
    DP[i+1][0]=max(DP[i][2],DP[i][3])+A[i]
    DP[i+1][1]=max(DP[i][0],DP[i][1])
    DP[i+1][2]=max(DP[i][0],DP[i][1])-A[i]
    DP[i+1][3]=max(DP[i][2],DP[i][3])
print(max(DP[N]))