use std::cmp::*;
use std::collections::*;
use std::io::*;
use std::str::FromStr;
fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}
fn main(){
    let n:usize = read();
    let m:usize = read();
    let mut a:Vec<i64> = vec![0;n];
    for i in 0..n{
        let mut rec:i64 = 0;
        for _j in 0..m {
            let l:i64 = read();
            rec += l;
        }
        a[i] = rec;
    }
    let mut dp:Vec<Vec<i64>> = vec![vec![0;2];n];
    dp[0][0] = a[0];
    for i in 1..n{
        dp[i][0] = max(dp[i - 1][1] + a[i],a[i]);
        dp[i][1] = max(dp[i - 1][0] - a[i],0);
    }
    let mut ans:i64 = 0;
    for i in 0..n{
        for j in 0..2{
            ans = max(ans,dp[i][j]);
        }
    }
    println!("{}",ans);
}