program ciur;
var f,g:text;
    n,nr,numar,k:longint;
    marcat:array [1..2000000] of boolean;
begin
 assign (f,'ciur.in'); reset (f);
 assign (g,'ciur.out'); rewrite (g);
 read (f,n);
 nr:=1; numar:=2; marcat[2]:=true;
 while numar<=n do
 begin
   k:=numar;
   while k<=n do
   begin
    marcat[k]:=true;
    k:=k+numar;
   end;
   while marcat[numar]=true do
    numar:=numar+1;
   nr:=nr+1;
 end;
 write (g,nr-1);
 close (f);
 close (g);
end.