#include <bits/stdc++.h>
using namespace std;
const int N=105;
int n,m,i,j,x,y,comp;
bool f[N];
stack<int> s;
vector<int> e[N],r[N];
void dfs1(int x)
{
    f[x]=1;
    for(auto y:e[x])
    {
        if(!f[y])
        {
            f[y]=1;
            dfs1(y);
        }
    }
    s.push(x);
}
int dfs2(int x)
{
    int s=1;
    f[x]=1;
    for(auto y:r[x])
    {
        if(!f[y])
        {
            f[y]=1;
            s+=dfs2(y);
        }
    }
    return s;
}
void kosaraju()
{
    int i,j;
    for(i=1;i<=n;++i)
    {
        if(!f[i]) dfs1(i);
    }
    for(i=1;i<=n;++i)
    {
        f[i]=0;
    }
    while(!s.empty())
    {
        int x=s.top();
        s.pop();
        if(!f[x])
        {
            if(dfs2(x)==1) ++comp;
           //cout<<dfs2(x)<<'\n';
        }
    }
}
int main()
{
    cin>>n>>m;
    while(m--)
    {
        cin>>x>>y;
        e[x].push_back(y);
        r[y].push_back(x);
    }
    kosaraju();
    cout<<comp;
    return 0;
}