# [Python 2], <s>108</s> <s>97</s> 89 bytes

<!-- language-all: lang-python -->

    i=input().split(".")
    for x in range(len(i)+~(i[-1][0]<"[")):i[x]=i[x][0]
    print".".join(i)

[Try it online!]

[Python 2]: https://docs.python.org/2/
[Try it online!]: https://tio.run/nexus/python2#FYwxDsMgEAR7vwJdBYpyctoorvKFdIgCWRhdQu4QYMlVvk5ws8VoZjstxHlv2mDNiZoGBDNtUtShiFXxHINOgTWZy0@Tvd6cnd0DLBhzJ3u45ZyBplyI26jxLXTqvcMqX4wiMQVMMo4KZr9@fAz4CrU9k68V/g "Python 2 – TIO Nexus"

-8 with many thanks to @ovs for the tip