#include<bits/stdc++.h>
using namespace std;
int n,m,a,b;
int ans;
bool book[205][205];
int belong[205];
bool used[205];
bool find(int x)
{
    for(int i=1;i<=n;i++)
    {
        if(used[i]||!book[x][i])
            continue;
        used[i]=1;
        if(!belong[i]||find(belong[i]))
        {
            belong[i]=x;
            return 1;
        }
    }
    return 0;
}
int main()
{
    cin>>n>>m;
    while(m--)
    {
        scanf("%d %d",&a,&b);
        book[a][b]=1;
    }
    for(int k=1;k<=n;k++)
        for(int i=1;i<=n;i++)
            for(int j=1;j<n;j++)
                if(book[i][k]&&book[k][j])
                    book[i][j]=1;
    for(int i=1;i<=n;i++)
    {
        memset(used,0,sizeof(used));
        if(find(i))
            ans++;
    }
    cout<<n-ans<<endl;
    return 0;
}