#![allow(unused_imports)]
#![allow(non_snake_case)]
use std::cmp::*;
use std::collections::*;
use std::io::Write;

#[allow(unused_macros)]
macro_rules! debug {
    ($($e:expr),*) => {
        #[cfg(debug_assertions)]
        $({
            let (e, mut err) = (stringify!($e), std::io::stderr());
            writeln!(err, "{} = {:?}", e, $e).unwrap()
        })*
    };
}

fn main() {
    let n = read::<usize>();
    let mut ab = vec![];
    for i in 0..n - 1 {
        let v = read_vec::<i64>();
        ab.push((v[0], v[1]));
    }
    let a_sum = ab.iter().map(|&x| x.0).sum::<i64>();
    let b_sum = ab.iter().map(|&x| x.1).sum::<i64>();
    let b_max = a_sum;
    let a_max = b_sum;
    let b_min = max(a_sum - b_sum, 0);
    let a_min = max(b_sum - a_sum, 0);
    println!("{}", min(b_max - b_min + 1, a_max - a_min + 1));
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}