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[] NMi => ReadLine().Split().Select(c => int.Parse(c) - 1).ToArray();
    static int[][] NMap(int n) => Enumerable.Repeat(0, n).Select(_ => NMi).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var c = NList;
        var (n, m) = (c[0], c[1]);
        var map = NMap(m);
        var from = new int[n];
        var to = new int[n];
        var uf = new UnionFindTree(n);
        foreach (var edge in map)
        {
            ++from[edge[0]];
            ++to[edge[1]];
            uf.Unite(edge[0], edge[1]);
        }
        var pts = new int[n];
        for (var i = 0; i < n; ++i) if (from[i] > to[i]) pts[uf.GetRoot(i)] += from[i] - to[i];
        var list = new List<int>();
        for (var i = 0; i < n; ++i) if (uf.GetRoot(i) == i && (uf.GetSize(i) > 1 || from[i] > 0))
        {
            list.Add(pts[i]);
        }
        var ans = list.Count - 1;
        foreach (var li in list) ans += Math.Max(0, li - 1);
        WriteLine(ans);
    }
    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)];
        }
    }
}