program ciur_erathosthenes;
type sir=array[1..2000000] of boolean;
var n,i,j,t,h:longint;
    s:sir;
    d,o:text;
begin
assign(d,'ciur.in');
assign(o,'ciur.out');
reset(d);rewrite(o);
read(d,n);
t:=n-1;
for i:=1 to n do s[i]:=true;
s[1]:=false;
for i:=2 to (n div 2) do
  begin
    if not(s[i]) then continue;
    j:=i*2;
    while j<=n do
      begin
        if s[j] then begin t:=t-1;s[j]:=false; end;
        j:=j+i;
      end;
  end;
write(o,t);
close(d);close(o);
end.