#![allow(unused_imports)]
#![allow(dead_code)]
#![allow(non_camel_case_types)]
#![allow(non_snake_case)]

use std::cmp::*;
use std::collections::*;
use std::ops::*;
use std::io::{Write, BufWriter};

const MOD: usize = 998244353;

// https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
macro_rules! input {
    ($($r:tt)*) => {
        let stdin = std::io::stdin();
        let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock()));
        let mut next = move || -> String{
            bytes
                .by_ref()
                .map(|r|r.unwrap() as char)
                .skip_while(|c|c.is_whitespace())
                .take_while(|c|!c.is_whitespace())
                .collect()
        };
        input_inner!{next, $($r)*}
    };
}

macro_rules! input_inner {
    ($next:expr) => {};
    ($next:expr, ) => {};

    ($next:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($next, $t);
        input_inner!{$next $($r)*}
    };
}

macro_rules! read_value {
    ($next:expr, ( $($t:tt),* )) => {
        ( $(read_value!($next, $t)),* )
    };

    ($next:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()
    };

    ($next:expr, chars) => {
        read_value!($next, String).chars().collect::<Vec<char>>()
    };

    ($next:expr, usize1) => {
        read_value!($next, usize) - 1
    };

    ($next:expr, [ $t:tt ]) => {{
        let len = read_value!($next, usize);
        (0..len).map(|_| read_value!($next, $t)).collect::<Vec<_>>()
    }};

    ($next:expr, $t:ty) => {
        $next().parse::<$t>().expect("Parse error")
    };
}

fn solve() {
    input! {
        n: usize,
        a: [[i32;2];n-1],
    }
    let mut ans = 0;
    let sum1 = a.iter().fold(0, |acc, x| acc+x[0]);
    let sum2 = a.iter().fold(0, |acc, x| acc+x[1]);
    for i in 0..400000{
        let x = i;
        let y = sum1 + x - sum2;
        if y < 0 {continue;}
        if x > sum2 {continue;}
        let mut flag = true;
        for j in 0..n-1{
            if a[j][0] > sum2 + y - a[j][1] {
                flag = false;
            }
        }
        if flag {ans+=1;}
    }
    println!("{}", ans);
}

fn main() {
    // In order to avoid potential stack overflow, spawn a new thread.
    let stack_size = 104_857_600; // 100 MB
    let thd = std::thread::Builder::new().stack_size(stack_size);
    thd.spawn(|| solve()).unwrap().join().unwrap();
}