No need to slurp the file. Process it line by line, remembering just the name:

my $name = q();
while (<>) {
    my @cols = split;
    if ('I-GPE' eq $cols[-1]) {
        $name .= $cols[0] . ' ';
    } else {
        print $name, "\n" if chop $name;
        $name = $cols[0] . ' ';
    }
}
# Do not forget to output the last name.
chop $name;
print "$name\n";
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