如何避免电报聊天机器人在频道聊天中接收和回答？

I'm writing an telegram bot with golang and I have some troubles. I receive chat table from user by updates. But my bot is also in a channel chat, so if someone chat in this channel, the bot will also rep to them. How can I avoid this?

my code:

bot, err := tgbotapi.NewBotAPI("BOT_TOKEN")
if err != nil {
    log.Panic(err)
}
var client Client
///////
//bot.Debug = true
///////
log.Printf("Authorized on account %s", bot.Self.UserName)
offset := rand.Intn(10000)
fmt.Println(offset)
u := tgbotapi.NewUpdate(offset)
u.Timeout = 360
//var IDSender int64
updates, err := bot.GetUpdatesChan(u)
for update := range updates {
    if update.Message == nil {
        continue
    }
    _IdSender := update.Message.Chat.ID
    Greeting := tgbotapi.NewMessage(_IdSender, "Hello!")
    bot.Send(Greeting)
}