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 tree = new List<int>[n];
        for (var i = 0; i < tree.Length; ++i) tree[i] = new List<int>();
        foreach (var edge in map) tree[edge[0]].Add(edge[1]);

        var starts = new int[n];
        var ends = new int[n];
        for (var i = 0; i < n; ++i)
        {
            while (tree[i].Count > 0)
            {
                ++starts[i];
                var pos = i;
                do
                {
                    var next = tree[pos][tree[pos].Count - 1];
                    tree[pos].RemoveAt(tree[pos].Count - 1);
                    pos = next;
                } while (tree[pos].Count > 0);
                ++ends[pos];
            }
        }
        for (var i = 0; i < n; ++i)
        {
            var rm = Math.Min(starts[i], ends[i]);
            starts[i] -= rm;
        }
        WriteLine(Math.Max(0, starts.Sum() - 1));
    }
}