Students participate in interest groups, such as thinking training, reading appreciation, music, and computers. According to regulations, each student can participate in a maximum of 4 interest groups, and at least 1 interest group. How many different choices are there?
同学们参加兴趣小组，思维训练、阅读欣赏、音乐、电脑，按规定每人最多参加4个兴趣小组，最少参加1个兴趣小组，共有多少种不同的选择？
<gadget id="calculator">4 + 6 + 4 + 1</gadget>
<output>15</output>

<result>15</result>