var a:array[1..2000100] of byte;
    i,n,j,nr:longint;
    f,g:text;
begin
assign(f,'ciur.in');reset(f);
assign(g,'ciur.out');rewrite(g);
 readln(f,n);
 nr:=0;
 for i:=2 to n do
  if a[i]=0 then begin
                  inc(nr);
                  for j:=2 to (n div 2) do
                   a[j*i]:=1;
                 end;
 write(g,nr);
close(f);
close(g);
end.