Strings in Character Land

$You$ $cannot$ $exist$ $forever$ $in$ $a$ $place$ $where$ $you$ $don't$ $belong$. Character Land is a strange place where only Characters can live.Whenever a String $S$ of length $N$ enters Character Land,it slowly reduces in length,until it becomes a character itself. Every Character in Character Land has a value. $A -> 0$ , $B -> 1$ , $C -> 2$ and so on. The reduction of Strings occur in a pecu