Найти ближайшую к a степень тройки (паскаль)

Var a, stepen1, stepen2: longint; beginclrscr; readln (a); stepen1: =1; while stepen1 <= a do stepen1: =stepen1*3; stepen2: =stepen div 3; if (a-stepen2) >=(stepen1-a) then writeln (stepen1) else writeln (stepen2); end.