program ciur;
 var n,nr,a,d:integer;
     ok:boolean;
     f,g:text;
Begin
 Assign(f,'ciur.in');reset(f);
 Assign(g,'ciur.out');rewrite(g);
 read(f,n);
 if n<2 then write(g,'0')
 else begin
   nr:=1;
   a:=3;
   while a<=n do begin
     ok:=true; d:=2;
     while ((d*d<=a) and ok) do begin
       if a mod d = 0 then ok:=false;
       d:=d+1;
     end;
     if ok then nr:=nr+1;
     a:=a+2;
   end;
   write(g,nr);
 end;
end.