fn main() {
    let mut xx = String::new();
    std::io::Read::read_to_string(&mut std::io::stdin(), &mut xx).ok();
    let xx: Vec<i64> = xx.split_whitespace().skip(1).flat_map(str::parse).collect();

    let n = xx.len() / 2;
    let diff: Vec<i64> = xx.chunks(2).map(|x| x[0] - x[1]).collect();

    let mut left = vec![0; n + 1];
    let mut right = vec![0; n + 1];
    left[1] = diff[0];
    right[n - 1] = -diff[n - 1];
    for i in 2..=n {
        left[i] = left[i - 1] + diff[i - 1];
        right[n - i] = right[n - i + 1] - diff[n - i];
    }

    let answer = (0..=n).map(|i| left[i] + right[i]).max().unwrap();

    println!("{answer}");
}