var a:array[1..2000000] of byte;
    i,n,k,rs,j:longint;

begin
 assign(input,'ciur.in');
 assign(output,'ciur.out');
 reset(input);
 rewrite(output);

  readln(n);
   for i:=2 to n do
    if a[i]=0 then begin
                    for j:=2 to n div i do
                     a[i*j]:=1;
                    end;

   for i:=2 to n do
    if a[i]=0 then inc(rs);

   writeln(rs);

 close(input);
 close(output);
{Totusi este trist in lume}
end.