Some parents and teachers accompanied primary school students to participate in a certain mathematics competition. Parents are father or mother, they are not teachers. It is known that the total number of parents, teachers and pupils is 30, of which the number of parents is more than half, mothers are more than fathers, pupils are 4 more than mothers, and there is at least one teacher. So among these 30 people, how many people are dads?
一些家长和老师陪同小学生参加某数学竞赛．家长为爸爸或者妈妈，他们都不是老师．已知家长、老师以及小学生的总人数为30，其中家长的人数超过一半，妈妈比爸爸多，小学生比妈妈多4人，至少有一个老师．那么在这30人中，爸爸有多少人？
<gadget id="calculator">9 + 4</gadget>
<output>13</output>

<gadget id="calculator">30 - 9 - 13 - 1</gadget>
<output>7</output>

<result>7</result>