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 uf = new UnionFindTree(200001);
        foreach (var arr in map) if (arr[0] != arr[1])
        {
            ++cin[arr[0]];
            ++cout[arr[1]];
            uf.Unite(arr[0], 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]);
            }
        }
        var roots = new HashSet<int>();
        foreach (var arr in map) roots.Add(uf.GetRoot(arr[0]));
        if (roots.Count > 1)
        {
            WriteLine(0);
        }
        else 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);
        }
    }
    class UnionFindTree
    {
        int[] roots;
        public UnionFindTree(int size)
        {
            roots = new int[size];
            for (var i = 0; i < size; ++i) roots[i] = -1;
        }
        public int GetRoot(int a)
        {
            if (roots[a] < 0) return a;
            return roots[a] = GetRoot(roots[a]);
        }
        public bool IsSameTree(int a, int b)
        {
            return GetRoot(a) == GetRoot(b);
        }
        public bool Unite(int a, int b)
        {
            var x = GetRoot(a);
            var y = GetRoot(b);
            if (x == y) return false;
            if (-roots[x] < -roots[y]) { var tmp = x; x = y; y = tmp; }
            roots[x] += roots[y];
            roots[y] = x;
            return true;
        }
        public int GetSize(int a)
        {
            return -roots[GetRoot(a)];
        }
    }
}