read n
read a
a=`echo -e "${a// /\n}" | sort -n | uniq -c`
head1=`echo "${a}" | awk 'NR==1 {print $1}'`
head2=`echo "${a}" | awk 'NR==1 {print $2}'`
end1=`echo "${a}" | awk 'END {print $1}'`
end2=`echo "${a}" | awk 'END {print $2}'`
if [ $head2 -eq 1 ]
then
	echo Impossible
	exit
else
	echo Possible
	exit
fi
