use std::io::Read;

fn run() {
    let mut s = String::new();
    std::io::stdin().read_to_string(&mut s).unwrap();
    let mut it = s.trim().split_whitespace();
    it.next();
    let a: Vec<i64> = it.map(|s| s.parse().unwrap()).collect();
    let mut sum = 0;
    for a in a.chunks_exact(2) {
        sum += a[1] - a[0];
    }
    let mut ans = sum;
    for a in a.chunks_exact(2) {
        sum += 2 * (a[0] - a[1]);
        ans = std::cmp::max(ans, sum);
    }
    println!("{}", ans);
}

fn main() {
    run();
}