#![allow(unused_imports)]
#![allow(non_snake_case)]
use std::cmp::*;
use std::collections::*;
use std::io::Write;

#[allow(unused_macros)]
macro_rules! debug {
    ($($e:expr),*) => {
        #[cfg(debug_assertions)]
        $({
            let (e, mut err) = (stringify!($e), std::io::stderr());
            writeln!(err, "{} = {:?}", e, $e).unwrap()
        })*
    };
}

fn main() {
    let v = read_vec::<usize>();
    let (n, m) = (v[0], v[1]);
    let mut a = vec![vec![0; m]; n];
    for i in 0..n {
        let v = read_vec::<i64>();
        for j in 0..m {
            a[i][j] += v[j];
        }
    }

    let a = a.iter().map(|x| x.iter().sum::<i64>()).collect::<Vec<_>>();

    let mut dp = vec![0; 2];
    dp[1] = -std::i64::MAX;
    for i in 0..n {
        dp[1] = max(dp[1], dp[0] + a[i]);
        if dp[1] != -std::i64::MAX {
            dp[0] = max(dp[0], dp[1] - a[i]);
        }
    }
    let ans = max(dp[0], dp[1]);
    println!("{}", ans);
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}