program dfs;
var A : array [1..100,1..100] of 0..1;
    viz : array [1..100] of 0..1;
    m,n,i,x,y,cnt : 0..100000;
    f : text;
procedure df(p:integer);
var k : 1..100000;
begin
viz[p] := 1;
for k := 1 to n do
if A[p,k]=1 then if viz[k]<>1 then df(k);
end;
begin
assign(f,'dfs.in');
reset(f);
readln(f,n,m);

for i := 1 to m do begin
readln(f,x,y);
A[x,y] := 1;
end;
close(f);
cnt := 0;
for i := 1 to n do
if viz[i]<>1 then begin
                  inc(cnt);
                  df(i);
                  end;

assign(f,'dfs.out');
rewrite(f);
write(f,cnt);
close(f);
end.