There are 78 seats in a bus. It starts empty. There is one passenger at the first stop, two passengers at the second stop, and three passengers at the third stop. How many stops will the bus be full of passengers?
一辆公共汽车有78个座位，空车出发，第一站上一位乘客，第二站上二位乘客，第三站上三位乘客，依次下去，多少站以后，车上坐满乘客？
<result>12</result>