program ciur;
var
 n,i,count,j:longint;
 v:array[1..2000000] of boolean;
 f,g:text;
begin
 assign(f,'ciur.in');
 assign(g,'ciur.out');
 reset(f);
 read(f,n);
 close(f);
 for i:=2 to n do
  begin
   if (not v[i]) and (i<=round(sqrt(n))) then
    begin
     inc(count);
     for j:=i to n div i do
       v[j*i]:=true;
    end;
   if (not v[i]) and (i>round(sqrt(n))) then
    inc(count);
  end;
 rewrite(g);
 write(g,count);
 close(g);
end.