uses math;
const
  fi='';//spa.inp';
  fo='';//spa.out';
  maxn=trunc(1e5);
  maxm=trunc(1e6);
  oo=trunc(1e9);
var
  i,j,n,m,tpltm,top,tg,count : longint;
  link,head,ke : array[1..maxm] of longint;
  low,num : array[1..maxn] of longint;
  st : array[1..maxm*10] of longint;
  cx : array[1..maxn] of boolean;
procedure add(i,u,v : longint);
  begin
    link[i] := head[u];
    head[u] := i;
    ke[i] := v;
  end;
procedure enter;
  var u,v : longint;
  begin
    assign(input,fi);reset(input);
    readln(n,m);
    for i:=1 to m do
      begin
        read(u,v);
        add(i,u,v);
      end;
  end;
function pop : longint;
  begin
    pop := st[top];
    dec(top);
  end;
procedure push(x : longint);
  begin
    inc(top);
    st[top] := x;
  end;
procedure dfs(u : longint);
  var i,v : longint;
  begin
    inc(count);
    num[u] := count;
    low[u] := count;
    push(u);
    i := head[u];
    while I<>0 do
      begin
        v := ke[i];
        if cx[v] then
        if num[v]=0 then
          begin
            dfs(v);
            low[u] := min(low[u],low[v]);
          end
          else
          begin
            low[u] := min(low[u],num[v]);
          end;
        i := link[i];
      end;
    if low[u]=num[u] then
      begin
        inc(tpltm);
        repeat
          v := pop;
          cx[v] := false;
        until v=u;
      end;
  end;
procedure process;
  var i : longint;
  begin
    fillchar(cx,sizeof(cx),true);
    for i:=1 to n do
      if num[i]=0 then
        begin
          dfs(i);
        end;
  end;
procedure print;
  begin
    assign(output,fo);rewrite(output);
    writeln(tpltm);
    close(output);
  end;
begin
  enter;
  process;
  print;
end.

uses math; const fi='';//spa.inp'; fo='';//spa.out'; maxn=trunc(1e5); maxm=trunc(1e6); oo=trunc(1e9); var i,j,n,m,tpltm,top,tg,count : longint; link,head,ke : array[1..maxm] of longint; low,num : array[1..maxn] of longint; st : array[1..maxm*10] of longint; cx : array[1..maxn] of boolean; procedure add(i,u,v : longint); begin link[i] := head[u]; head[u] := i; ke[i] := v; end; procedure enter; var u,v : longint; begin assign(input,fi);reset(input); readln(n,m); for i:=1 to m do begin read(u,v); add(i,u,v); end; end; function pop : longint; begin pop := st[top]; dec(top); end; procedure push(x : longint); begin inc(top); st[top] := x; end; procedure dfs(u : longint); var i,v : longint; begin inc(count); num[u] := count; low[u] := count; push(u); i := head[u]; while I<>0 do begin v := ke[i]; if cx[v] then if num[v]=0 then begin dfs(v); low[u] := min(low[u],low[v]); end else begin low[u] := min(low[u],num[v]); end; i := link[i]; end; if low[u]=num[u] then begin inc(tpltm); repeat v := pop; cx[v] := false; until v=u; end; end; procedure process; var i : longint; begin fillchar(cx,sizeof(cx),true); for i:=1 to n do if num[i]=0 then begin dfs(i); end; end; procedure print; begin assign(output,fo);rewrite(output); writeln(tpltm); close(output); end; begin enter; process; print; end.