program ciur_erat;
type ciur=array[1..2000000] of boolean;
var f,g:text;
    x:ciur;
    i,k,n,nr:longint;
begin
assign (f,'ciur.in'); reset (f);
assign (g,'ciur.out'); rewrite (g);
readln (f,n);
nr:=0;
for i:=1 to n do x[i]:=true;
for i:=3 to n do
   if (x[i]) then begin nr:=nr+1;
                        k:=2*i;
                        while (k<=n) do begin x[k]:=false;
                                              k:=k+i;
                                        end;
                  end;
write (g,nr);
close (f);
close (g);
end.