Triggering a lambda when a new ami is available

For exiting AMI its fine, But when new AMI is being create How to automate this , cause we dont know the arn before hand

The AMI ARN is included in the event.

{
    "version": "0",
    "id": "example-9f07-51db-246b-d8b8441bcdf0",
    "detail-type": "EC2 AMI State Change",
    "source": "aws.ec2",
    "account": "012345678901",
    "time": "yyyy-mm-ddThh:mm:ssZ",
    "region": "us-east-1",
    "resources": ["arn:aws:ec2:us-east-1::image/ami-0123456789example"],
    "detail": {
        "RequestId": "example-9dcc-40a6-aa77-7ce457d5442b",
        "ImageId": "ami-0123456789example",
        "State": "available",
        "ErrorMessage": ""
    }
}