N,M = map(int,input().split())
lsA = [0]
for i in range(N):
    lsA.append(sum(list(map(int,input().split()))))
#dp[i][j]=i番目までの最大値とったのが偶数番目奇数番目か(j=0,1)
dp = [[0,0] for i in range(N+1)]
dp[0][1] = -float('INF')
for i in range(1,N+1):
    dp[i][0] = max(dp[i-1][1]-lsA[i],dp[i-1][0])
    dp[i][1] = max(dp[i-1][0]+lsA[i],dp[i-1][1])
print(max(dp[N][0],dp[N][1]))