#!/bin/bash

read n
read -p -a arr

mx=0
cnt=0
vis=()
for i in ${arr[@]}; do
    vis[$i]=$((${vis[$i]} + 1))
    if [[ $mx -lt $i ]]; then
        mx=$i
        cnt=1
    elif [[ $mx -eq $i ]]; then
        cnt=$(($cnt + 1))
    fi
done

for (( i = $(( $mx / 2 + 1 )) ; i <= $mx ; i++ )) do
    if [[ -z ${vis[$i]} ]]; then
        echo "Impossible"
        exit
    elif [[ ${vis[$i]} -lt 2 ]];then
        echo "Impossible"
        exit
    fi
done

if [[ $(($mx % 2)) -eq 0 ]];then
    half=$(( $mx / 2 ))
    if [[ -z ${vis[$half]} ]];then
        echo "Impossible"
        exit
    elif [[ ${vis[$half]} -ne 1 ]];then
        echo "Impossible"
        exit
    fi
fi

for (( i = $(( ($mx - 1) / 2 )) ; i >= 1; i-- )) do
    if [[ -n ${vis[$i]} ]];then
        echo "Impossible"
        exit
    fi
done

echo "Possible"