using System;
using System.Linq;
using System.Collections.Generic;
using System.IO;

class MyClass
{
    public static void Solve()
    {
        var N = int.Parse(Console.ReadLine());
        var A = new int[N];
        var B = new int[N];
        for (int i = 1; i < N; i++)
        {
            var input = Console.ReadLine().Split().Select(int.Parse).ToArray();
            A[i] = input[0];
            B[i] = input[1];
        }
        var sumA = A.Sum();
        var sumB = B.Sum();
        var diff = sumB - sumA;
        if (diff >= 0)
        {
            Console.WriteLine(sumB - diff + 1);
        }
        else
        {
            Console.WriteLine(sumA + diff + 1);
        }
    }

    public static void Main()
    {
        var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
        Console.SetOut(sw);
        Solve();
        Console.Out.Flush();
    }
}