Telegram Bot HandbookHow IDs of Users and Chats Work
Each user, bot, group, or channel has an invariable ID.
Official Telegram apps don't show IDs. Use unofficial apps or bots like this when you need to manually learn specific user or chat IDs.
WARNING
Don't store user and chat IDs in 32-bit integers: they may be too large. Double-precision floats (such as number in JS) or 64-bit integers are OK.
In Bot API
In Bot API, regular group IDs start with - and supergroup IDs start with -100. Thus, a channel with an actual ID 1356415630 has ID -1001356415630 in Bot API.
Bot ID in its token
The first part of a bot token is the bot ID. For example, the token 110201874:AAHdqTcvCH1vGWJxfSeofSAs0K5PALDsaw belongs to the bot with ID 110201874.