The 400-meter race enters the sprint stage. A is 30 meters in front of B, C is 60 meters behind D, and B is 20 meters in front of C. At this time, how many meters is the difference between the two students running in front?
四百米比赛进入冲刺阶段，甲在乙前面30米，丙在丁后面60米，乙在丙前面20米．这时，跑在前面的两位同学相差多少米．
<gadget id="calculator">60 - 20 - 30</gadget>
<output>10</output>

<result>10</result>