阅读理解     

 My name is Dora.I’m American and I’m thirteen.I’m a student in No.7 Middle School.I like music very much.I can play two instruments— the guitar and the piano.I play them very well and I’m on the school art club.

Jeff and Michael are my brothers.They are students,too .But we aren’t in the same school.They like sports.Jeff plays basketball and soccer           very well.Michael swims and plays ping-pong very  well.I am not good at sports.They help me with sports after school.

We live in London with our parents now.My mother is an English teacher and my father is a musician.My mother swims well.My father can play the violin.

已知x，y满足约束条件$\left\{\begin{array}{c}x-y+5\ge 0\\ x+y\ge 0\\ x\le 3\end{array}\right.$则z=2x+y的最小值为____