using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var n = NN;
        var map = NArr(n);
        var cin = new int[200001];
        var cout = new int[200001];
        var eq = new int[200001];
        foreach (var arr in map) if (arr[0] != arr[1])
        {
            ++cin[arr[0]];
            ++cout[arr[1]];
        }
        var scount = 0;
        for (var i = 0; i < cin.Length; ++i)
        {
            if (cin[i] != cout[i])
            {
                scount += Math.Max(0, cin[i] - cout[i]);
            }
        }
        if (scount == 0)
        {
            var set = new HashSet<int>(map.Select(mi => mi[0]));
            WriteLine(set.Count);
        }
        else if (scount == 1)
        {
            WriteLine(1);
        }
        else
        {
            WriteLine(0);
        }
    }
}