update: I missed the fact that the string of digits with periods needs to be extracted from a line of additional text. The solution I posted below would only work once you have already extracted the digit/period string.

# why use a regex? splitting is enough
while ( <DATA> ) {
    print $_ if ( (split( /\./ ))[2] > 3 );
}

__DATA__
0.1.1.1
0.1.2.2
0.1.3.3
0.1.10.1
0.1.20.2
0.1.30.3
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