program p43;
var m,p:longint;f,g:text;
function ciur(n:longint):longint;
var  i,j,s:longint;
    v:array[1..50000]of boolean;
begin
 s:=0;
   for i:=2 to n do
    if not (v[i]) then begin
    s:=s+1;
     for j:=2 to n div i do
     v[i*j]:=true;
     end;ciur:=s;end;
begin
     assign(f,'ciur.in');reset(f);
     assign(g,'ciur.out');rewrite(g);
     read(f,m); p:=ciur(m);
     write(g,p);close(f);close(g);
     end.