var n,m,i,j,k,s1,s2,ans,x,y:longint;
    a,u:array[1..100,1..100]of boolean;
begin
 readln(n,m);
 fillchar(a,sizeof(a),false);
 fillchar(u,sizeof(u),false);
 for i:=1 to m do begin
  readln(x,y);
  a[x,y]:=true;
  u[y,x]:=true;
 end;
 for k:=1 to n do
  for i:=1 to n do
   for j:=1 to n do
    if (i<>j)and(j<>k)and(i<>k) then begin
     a[i,j]:=a[i,j]or((a[i,k])and(a[k,j]));
     u[i,j]:=u[i,j]or((u[i,k])and(u[k,j]));
     end;
  for i:=1 to n do begin
   s1:=0; s2:=0;
   for j:=1 to n do begin
    if (i<>j)and(a[i,j]) then inc(s1);
    if (i<>j)and(u[i,j]) then inc(s2);
   end;
   if (s1>(n-1)div 2)or(s2>(n-1)div 2)then inc(ans);
  end;
 writeln(ans);
end.