const
  alf = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ';

  function power(x,y: integer): int64;
  begin
    if x = 0 then
      result := 0
    else
      result := trunc(exp(ln(x)*y));
  end;

  function fromdec(d: int64; s: integer): string;
  begin
    if (d < s) then
      result := alf[d + 1]
    else
      result := fromdec(d div s,s) + alf[d mod s + 1];
  end;

  function todec(d: string; s: integer): int64;
  begin
    if length(d) = 1 then
      result := pos(d,alf) - 1
    else
      result := (pos(d[1],alf) - 1) * power(s, length(d)-1) + todec(copy(d,2,length(d)-1),s);
  end;