There are several beads of four colors: red, yellow, blue, and green. Each person can choose 3 of them. It is necessary to ensure that there are at least five beads of the same color. How many people must participate?
有红、黄、蓝、绿四种颜色的珠子若干颗，每个人可以从中任选3颗，要保证至少有五个人选的珠子的颜色完全相同，至少要有多少人参加？
<gadget id="calculator">20 * 4</gadget>
<output>80</output>

<gadget id="calculator">80 + 1</gadget>
<output>81</output>

<result>81</result>