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