program ciurul_lui_eratostene;
var prim:array[1..2000000] of byte;
    i,n,nr,j
    :longint;
    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 prim[i]=0 then
   begin
    nr:=nr+1;
    j:=i+i;
    while j<=n do
     begin
      prim[j]:=1;
      j:=j+i;
     end;
   end;
 writeln(g,nr);
 close(f);
 close(g);
end.