var b:array[2..2000001] of boolean;
  i,j:                     longint;
    t:                        text;
  s,n:                     longint;
       begin
        assign(t,'ciur.in');
        reset(t);
        readln(t,n);
        close(t);
        j:=1;s:=0;
        while (sqr(j)<=n) do begin
          inc(j);
          if not(b[j]) then begin
             i:=sqr(j);
             while (i<n) do begin
               b[i]:=true;
               i:=i+j;
             end;
          end;
        while (j<n) do begin
          inc(j);
          if not(b[j]) then inc(s);
        end;
          if not(b[j]) then inc(s);
        end;
        assign(t,'ciur.out');
        rewrite(t);
        writeln(t,s);
        close(t);
       end.