let group = DispatchGroup()
var text = ""
for i in 0..<20 {
    group.enter()
    fetchData(i, delay: Double.random(in: 0...0.2)) {
        text += "\($0) - "
        group.leave()
    }
}
group.notify(queue: DispatchQueue.main) {
    print(text)
    exit(0)
}

RunLoop.current.run()