var     a:array[1..100000] of longint;
        b:array[1..100000] of boolean;
        n,m,x,y,i,j,k,nr:longint;
        f,g:text;

procedure sort(var a,b:longint);
var     t:longint;
begin
  if a>b then
    begin
      t:=a;
      a:=b;
      b:=t;
    end;
end;

begin
  assign(f,'dfs.in');
  reset(f);
  assign(g,'dfs.out');
  rewrite(g);
  readln(f,n,m);

 { for i:=1 to n do
    a[i]:=i;

  for i:=1 to m do
    begin
      readln(f,x,y);
      k:=a[y];
      for j:=1 to n do
        if a[j]=k then a[j]:=a[x];
    end;
  for i:=1 to n do
    if not b[a[i]] then
      begin
        inc(nr);
        b[a[i]]:=true;
      end;}


  for i:=1 to n do
    b[i]:=true;

  for j:=1 to m do
    begin
      readln(f,x,y);
      sort(x,y);
      b[y]:=false;
    end;

  nr:=0;
  for i:=1 to n do
    if b[i] then inc(nr);
  writeln(g,nr);
  close(g);
end.