use std::cmp::max;

fn main() {
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).ok();
    let n: usize = n.trim().parse().unwrap();
    let mut a = String::new();
    std::io::stdin().read_line(&mut a).ok();
    let a: Vec<isize> = a.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();

    let backs: Vec<isize> = (0..n).map(|i| a[2*i as usize +1] - a[2*i as usize]).collect();
    let fronts: Vec<isize> = (0..n).map(|i| a[2*i as usize] - a[2*i as usize +1]).collect();
    let mut max_val: isize = -1_000_000_000_000_000_000;
    let mut front_val: isize = 0;
    let mut back_val: isize = backs.iter().map(|i| *i).sum();
    for i in 0..=n {
        max_val = max(max_val, front_val + back_val);
        if i < n {
            front_val += fronts[i];
            back_val -= backs[i];
        }
    }
    println!("{}", max_val);
}