so 9999 - lirik i love you so maher zain

So 9999 repesents 1km backwards, or -1 km. If you add 1km to this number you get 10000. But since you only have four digits, you end up with 0000. So -1km + 1km indeed results in 0km. You sill need a way to distinguish whether 9999 is 9999 km forwards or 1 km backwards. This is merely a matter of convention. say so