Given a string, find the shortest possible string which can be achieved by adding characters to the end of initial string to make it a palindrome.

function buildPalindrome(st: string): string {
    let reversed = st.split("").reverse().join("");
    let counter = st.length;
    while(st !== reversed){
        if(st.slice(0,counter) === reversed.slice(0,counter)){
            return st + reversed.slice(counter-1);
        }
        counter--;
    }
    return st;
}