def main():
    import sys
    input=sys.stdin.buffer.readline
    n,m=map(int,input().split())
    a=[sum(list(map(int,input().split()))) for _ in range(n)]
    dp=[[-float('inf')]*(n+1) for _ in range(2)]
    dp[0][0]=0
    for i in range(n):
        dp[0][i+1]=max(dp[0][i],dp[1][i]-a[i])
        dp[1][i+1]=max(dp[1][i],dp[0][i]+a[i])
    print(max(dp[0][n],dp[1][n]))
main()