import java.io.IOException;
import java.io.InputStream;
import java.util.NoSuchElementException;
import java.util.TreeMap;
import static java.util.Comparator.reverseOrder;
import static java.util.Objects.nonNull;

public class Main {
    public static void main(String[] args) {
        FastScanner fsc = new FastScanner();
        int n = fsc.nextInt();
        int[] a = new int[n];
        TreeMap<Integer, Integer> map = new TreeMap<>(reverseOrder());
        for (int i = 0; i < n; i++) {
            a[i] = fsc.nextInt();
            Integer v = map.putIfAbsent(a[i], 1);
            if (nonNull(v)) {
                map.put(a[i], v + 1);
            }
        }
        int max = map.firstKey();
        int min = (max + 1) >> 1;
        boolean possible = true;
        for (int k = max; k >= 1; k--) {
            if (map.containsKey(k)) {
                int v = map.get(k);
                if (k > min) {
                    if (v <= 1) {
                        possible = false;
                    }
                } else if (k == min) {
                    if ((max & 1) != 0) {
                        if (v > 2) {
                            possible = false;
                        }
                    } else {
                        if (v > 1) {
                            possible = false;
                        }
                    }
                } else {
                    possible = false;
                }
            } else if (k >= min) {
                possible = false;
            }
        }
        System.out.println(possible ? "Possible" : "Impossible");
    }
}


class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;
    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        }else{
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }
    private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;}
    private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;}
    public boolean hasNext() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; return hasNextByte();}
    public String next() {
        if (!hasNext()) throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while(isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }
    public long nextLong() {
        if (!hasNext()) throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while(true){
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            }else if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }
    public int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException();
        return (int) nl;
    }
    public double nextDouble() { return Double.parseDouble(next());}
}


Measured memory_bytes: 22996