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: Vec<usize> = vec![];
    let mut p: Vec<usize> = vec![];
    for _ in 0..n {
        let mut pa = String::new();
        std::io::stdin().read_line(&mut pa).ok();
        let pa: Vec<usize> = pa.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
        p.push(pa[0]);
        a.push(pa[1]);
    }

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