#include<cstdio>
#include<vector>
using namespace std;
vector<int> v[100001];
int n,m,sqq;
int vec[100001],vc[100001];
void dfs(int x)
    {int i;
    for(i=0;i<v[x].size();i++)
        if(vec[v[x][i]]!=sqq)
            {vec[v[x][i]]=sqq;
            dfs(v[x][i]);
            }
    }
int main ()
{freopen ("dfs.in","r",stdin);
freopen ("dfs.out","w",stdout);
int i,x,y,k=0;
scanf("%d%d",&n,&m);
for(i=1;i<=n;i++)
    vec[i]=i;
for(i=1;i<=m;i++)
    {scanf("%d%d",&x,&y);
    v[x].push_back(y);
    }
for(i=1;i<=n;i++)
    if(vec[i]==i)
        {sqq=i;
        dfs(i);
        }
for(i=1;i<=n;i++)
    if(vc[vec[i]]==0)
        {vc[vec[i]]=1;
        k++;
        }
printf("%d",k);
return 0;
}