use std::cmp::max;

fn main() {
    let mut nm = String::new();
    std::io::stdin().read_line(&mut nm).ok();
    let nm: Vec<i64> = nm.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let n = nm[0];
    let mut a: Vec<i64> = vec![];
    for _ in 0..n {
        let mut tempa = String::new();
        std::io::stdin().read_line(&mut tempa).ok();
        let tempa: i64 = tempa.trim().split_whitespace().map(|s| s.parse::<i64>().unwrap()).sum::<i64>();
        a.push(tempa);
    }

    let mut dp: Vec<Vec<i64>> = vec![vec![0; n as usize + 1]; 2];
    for i in 0..(n as usize) {
        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]);
    }
    println!("{}", dp[0][n as usize]);
}