slack user-id

I have created a bot and integrated with slack following the instructions. The bot works as expected and posts to a lambda for fulfilment.

In the lambda i see as part of the request:'x-amz-lex:user-id' which i expect to be the slack user id but its not in the normal slack format of something like UXXXXXX but is a long int such as 'x-amz-lex:user-id': '396498713242.12.691123599936'. How do i translate this to the real slack userid so i can look up the profile for that user?

thanks

Andrew