import java.util.*;
import java.io.*;

public class Main {
    static long[] snacks;
    static long[][] dp;
	public static void main (String[] args) throws Exception{
    	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    	String[] first = br.readLine().split(" ", 2);
    	int n = Integer.parseInt(first[0]);
     	int m = Integer.parseInt(first[1]);
     	snacks = new long[n];
     	for (int i = 0; i < n; i++) {
     	    String[] line = br.readLine().split(" ", m);
     	    for (int j = 0; j < m; j++) {
     	        snacks[i] += Long.parseLong(line[j]);
     	    }
     	}
     	dp = new long[n][2];
     	for (long[] arr : dp) {
     	    Arrays.fill(arr, Long.MIN_VALUE / 10);
     	}
     	System.out.println(Math.max(dfw(n - 1, 0), dfw(n - 1, 1)));
    }
    
    static long dfw(int idx, int evod) {
        if (idx < 0) {
            if (evod == 0) {
                return 0;
            } else {
                return Long.MIN_VALUE / 10;
            }
        }
        if (dp[idx][evod] == Long.MIN_VALUE / 10) {
            if (evod == 0) {
                dp[idx][evod] = Math.max(dfw(idx - 1, 0), dfw(idx - 1, 1) - snacks[idx]);
            } else {
                dp[idx][evod] = Math.max(dfw(idx - 1, 1), dfw(idx - 1, 0) + snacks[idx]);
            }
        }
        return dp[idx][evod];
    }
}