program ciur2;
var N,i,j,rez:longint;
    v:array[1..2000000] of boolean;
    f,g:Text;
  begin
   assign(f,'ciur.in');reset(f);
   assign(g,'ciur.out');rewrite(g);

   readln(f,N);

   for i:=2 to N do
     if (not v[i]) then
       begin
         inc(rez);
         j := 2*i;
         while (j<=N) do
          begin
           v[j]:=true;
           j := j + i;
          end;
       end;
   writeln(g,rez);
   close(f);
   close(g);
  end.