#include <iostream.h>
#include <fstream.h>

ifstream fin("dfs.in");
ofstream fout("dfs.out");


char v[100005];
long n,nc,m,i;
char a[1005][1005];


void dfs(int i)
{int j;
v[i]=1;
for (j=1;j<=n;j++)
 if (v[j]==0 && a[i][j]==1)
  dfs(j);

}

int main()
{int x,y;
 fin>>n>>m;
 for (i=1;i<=m;i++)
 {fin>>x>>y;
  a[x][y]=1;
 }

for (i=1;i<=n;i++)
if (v[i]==0) {nc++; dfs(i);}

fout<<nc;
fout.close();
return 0;
}