var a sync.WaitGroup
var b sync.WaitGroup
var c sync.WaitGroup
a.Add(1)
go func() {
fmt.Println("1")
b.Add(1)
b.Wait()
a.Done()
}()
go func() {
fmt.Println("2")
c.Add(1)
c.Wait()
b.Done()
}()
go func() {
fmt.Println("3")
c.Done()
}()
a.Wait()
