var f,g:text; p,n,m,r:longint;
begin
  assign(f, 'fact.in');
  assign(g, 'fact.out');
  reset(f);
  rewrite(g);
  readln(f,p);
  n:=0;
  while r<p do
    begin
        inc(n);
        m:=n;
        while m mod 5=0 do
            begin
                inc(r);
                m:=m div 5
            end;
    end;
  write(g, n);
  close(f); close(g);

end.