"2 3 4 * 5 / +" --> 2 + 3 * 4 / 5 "3 4 * 5 / 2 +" --> 3 * 4 / 5 + 2 "3 4 5 / * 2 +" --> 3 * 4 / 5 + 2 "2 3 + 4 * 5 /" --> (2 + 3) * 4 / 5