import java.util.Arrays;
import java.io.BufferedWriter;
import java.util.InputMismatchException;
import java.io.InputStream;
import java.util.NoSuchElementException;
import java.io.OutputStreamWriter;
import java.math.BigInteger;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.io.Writer;
import java.io.IOException;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 * @author ogiekako
 */
public class Main {
	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		MyScanner in = new MyScanner(inputStream);
		MyPrintWriter out = new MyPrintWriter(outputStream);
		TaskC solver = new TaskC();
		solver.solve(1, in, out);
		out.close();
	}
}

class TaskC {
    public void solve(int testNumber, MyScanner in, MyPrintWriter out) {
        int n = in.nextInt();
        int[] cnt = new int[101];
        for (int i = 0; i < n; i++) cnt[in.nextInt()]++;
        out.println(solve(cnt) ? "Possible":"Impossible");
    }

    private boolean solve(int[] cnt) {
        int m = 0;
        for (int i = 0; i < 101; i++) if (cnt[i] > 0) m = i;
        int s = (m + 1) / 2;
        for (int i = 0; i < s; i++) if (cnt[i] > 0) return false;
        if (s * 2 == m) {
            cnt[s]--;
        } else {
            cnt[s] -= 2;
        }
        if (cnt[s] > 0) return false;
        for (int i = s + 1; i <= m; i++) cnt[i] -= 2;
        for (int i = 0; i < 101; i++) if (cnt[i] < 0) return false;
        return true;
    }
}

class MyScanner {
    private final InputStream in;

    public MyScanner(InputStream in) {
        this.in = in;
    }

    private static final int BUFSIZE = 65536;
    int bufLen;
    int bufPtr;
    byte[] buf = new byte[BUFSIZE];

    public int read() {
        if (bufLen == -1)
            throw new InputMismatchException();
        if (bufPtr >= bufLen) {
            bufPtr = 0;
            try {
                bufLen = in.read(buf);
            } catch (IOException e) {
                throw new InputMismatchException();
            }
            if (bufLen <= 0)
                return -1;
        }
        return buf[bufPtr++];
    }

    public int nextInt() {
        int c = read();
        if (c == -1) throw new NoSuchElementException();
        while (c != '-' && (c < '0' || '9' < c)) {
            c = read();
            if (c == -1) throw new NoSuchElementException();
        }
        if (c == '-') return -nextInt();
        int res = 0;
        do {
            res *= 10;
            res += c - '0';
            c = read();
        } while ('0' <= c && c <= '9');
        return res;
    }

}

class MyPrintWriter {
    PrintWriter out;

    public MyPrintWriter(OutputStream outputStream) {
        out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
    }

    public void println(Object... os) {
        if (os.length == 0) {
            out.println();
            return;
        }
        for (int i = 0; i < os.length - 1; i++) {
            out.print(os[i]);
            out.print(' ');
        }
        out.println(os[os.length - 1]);
    }

    public void close() {
        out.close();
    }

}



Measured memory_bytes: 8404