var n,i,x,c:longword;
        b,k:text;
        t:array[1..20000000]of byte;

begin

        assign(b,'ciur.in');
        assign(k,'ciur.out');

        reset(b);
        rewrite(k);

        readln(b,n);

        c:=0;

        for i:=2 to n do
                if t[i]=0 then begin inc(c);
                                     x:=i;
                                     while x+i<=n do begin
                                        x:=x+i;
                                        t[x]:=1;
                                                end;
                               end;

        writeln(k,c);

        close(b);
        close(k);

end.