Translate perl regular expression parsing to C#

I'm new to both Perl and regular expressions.  I have a messy data file that I need to "neaten".  I've been given a simple Perl script that accomplishes the task and need to translate this script into C# code.  Here's the important part of the script:

while (<INPUTFILE>) {
print OUTPUTFILE "$2+$4+$5\n"
if m@([^0-9]*)(1[0-9]{11}|[0-9]{11})([^0-9]*)([0-9]{4}/[0-9]{2}/[0-9]{2}) ([0-9]{2}:[0-9]{2}:[0-9]{2})@;
}

With no perl background and very little regular expression background, I'm having trouble figuring out what's what here.  C# has regular expression handling via Regex but I'm having trouble converting this to that.  Any help much appreciated!