PROGRAM Hello;

USES
	URadixSort;

VAR
	filein : text;
	mychar : char;
	myseat, column, row, pass, i, n : integer;
	seats : array[0..1023] of LongInt;

BEGIN
	myseat := 0;
	column := 0;
	row := 0;
	i := 0;

	assign(filein, 'input');
	reset(filein);
	repeat begin
			read(filein, mychar);

			case mychar of
				'F': row := row shl 1;
				'B': row := (row shl 1) or 1;
				'L': column := column shl 1;
				'R': column := (column shl 1) or 1;
				otherwise begin
					pass := row * 8 + column;
	
					seats[i] := pass;

					i := i + 1;
					row := 0;
					column := 0;
				end
			end;
		end;
	until eof(filein);
	close(filein);

	(* Thank god the wiki for this *)
	RadixSort(seats);

	for n := 1 to i do
		begin
			if seats[n] <> seats[n - 1] + 1 then
				myseat := seats[n] - 1
		end;

	writeln('Your seat is ', myseat);
END.