#include <iostream>
#include <fstream>

using namespace std;
ifstream fin("dfs.in");
ofstream fout("dfs.out");
int v[100000],n,m;
typedef struct{int x,y}M;
M u[200000];
void citire()
{int i,x,y;
fin>>n>>m;
for(i=1;i<=m;i++)
fin>>u[i].x>>u[i].y

}
void df(int s)
{int i,j;
v[s]=1;
for(i=1;i<=n;i++)
    if(u[s].x!=0&&u[i].y!=0&&v[i]==0)
    df(i);
}

int main()
{int k=0,i;
citire();
for(i=1;i<=n;i++)
    if(v[i]==0)
{k++;
 df(i);
}
fout<<k;
fin.close();
fout.close();
    return 0;
}