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
	if [ $head1 -ne 1 ]
	then
		echo Possible
		exit
	elif [ $end2 -eq 2 ]
	then
		echo Impossible
		exit
	fi
fi

if [ $end2 -eq $(( n - 1 )) ]
then
	gusukisu=$(( n % 2 ))
	if [ $gusukisu -eq 0 ]
	then
		if [ "`echo "${a}" | awk '{print $1}' | sort -u`" = "2" ]
		then
			echo Possible
			exit
		else
			echo Impossible
			exit
		fi
	else
		if [ $head1 -eq 1 -a $head2 -eq $(( n / 2 )) ]
		then
			if [ `echo "${a}" | wc -l` -eq $(( n / 2 + 1 )) ]
			then
				echo Possible
				exit
			else
				echo Impossible
				exit
			fi
		else
			echo Impossible
			exit
		fi
	fi
fi
