use strict;
use warnings;

local $/ = '>';

while (<>) {
	chomp;
	/\S/ or next;
	my ( $id, $seq ) = /(.+?)\n(.+)/s;
	$seq =~ s/\n//g;

	my $GCcount = $seq =~ tr/GC//;
	printf "%s, %.2f%%\n", ">$id", ( $GCcount / length $seq ) * 100;
}