Regex to extract number from text

Elastic Stack Elasticsearch
1

I want to extract number of Milliseconds from below text with regex (i.e extract 762 from in [762] Millies )

2019-07-02 16:56:44.824 [SUBSCRIBER_PROFILE-1115501650-9f7a9309-6bd7-44fb-83ea-2ee0ff37a50d] Response [<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<subscriberProfileResponse>
    <errorCode>99999</errorCode>
    <responseStatus>FAILED</responseStatus>
</subscriberProfileResponse>
] in [762] Millies.
2

Where do you want to run that? In logstash? In an ingest pipeline? What did you try so far?