#include<stdio.h>
FILE *f,*g;
long n,m,t[3][200005],i,x,y,c[100005],nr,v,viz[100005],plus1[100005],plus2[100005],tt[3][200005],ct[100005],nrt,j;
int dfs1(long i)
{ plus1[i]=x; v=c[i]; if(v!=0) dfs1(t[1][v]);
  v=c[i];
  while(v!=0)
   { v=t[2][v];
     if(plus1[t[1][v]]!=x) dfs1(t[1][v]);
   }
  return 0;
}
int dfs2(long i)
{ plus2[i]=x; v=ct[i]; if(v!=0) dfs2(tt[1][v]);
  v=ct[i];
  while(v!=0)
   { v=tt[2][v];
     if(plus2[tt[1][v]]!=x) dfs2(tt[1][v]);
   }
  return 0;
}
int main()
{ f=fopen("dfs.in","r"); g=fopen("dfs.out","w");
  fscanf(f,"%ld%ld",&n,&m);
  t[1][0]=1; tt[1][0]=1;
  for(i=1;i<=m;i++)
   { fscanf(f,"%ld%ld",&x,&y);
     if(!c[x])
      { while(t[1][nr]!=0) nr++;
	c[x]=nr;
	t[1][nr]=y;
      }
     else
      { v=c[x];
	while(t[2][v]!=0) v=t[2][v];
	while(t[1][nr]!=0) nr++;
	t[2][v]=nr; t[1][nr]=y;
      }
     v=x; x=y; y=v;
     if(!ct[x])
      { while(tt[1][nrt]!=0) nrt++;
	ct[x]=nrt;
	tt[1][nr]=y;
      }
     else
      { v=ct[x];
	while(tt[2][v]!=0) v=tt[2][v];
	while(tt[1][nrt]!=0) nrt++;
	tt[2][v]=nrt; tt[1][nrt]=y;
      }
   }
  nr=0; x=0; t[1][0]=0; tt[1][0]=0;
  for(i=1;i<=n;i++)
   { if(!viz[i])
      { nr++;
	x++; dfs1(i); dfs2(i);
	for(j=1;j<=n;j++) if(plus1[j]==x&&plus2[j]==x) viz[j]=1;
      }
   }
  fprintf(g,"%ld",nr); fclose(g);
  return 0;
}