Everybody knows what an arithmetic progression is. Let us remind you just in case that an arithmetic progression is such sequence of numbers a1, a2, ..., an of length n, that the following condition fulfills: 

a2 - a1 = a3 - a2 = a4 - a3 = ... = ai + 1 - ai = ... = an - an - 1.

For example, sequences [1, 5], [10], [5, 4, 3] are arithmetic progressions and sequences [1, 3, 2], [1, 2, 4] are not.

Alexander has n cards containing integers. Arthur wants to give Alexander exactly one more card with a number so that he could use the resulting n + 1 cards to make an arithmetic progression (Alexander has to use all of his cards).

Arthur has already bought a card but he hasn't written a number on it. Help him, print all integers that you can write on a card so that the described condition fulfilled.

Input

The first line contains integer n (1 ≤ n ≤ 105) — the number of cards. The next line contains the sequence of integers — the numbers on Alexander's cards. The numbers are positive integers, each of them doesn't exceed 108.

Output

If Arthur can write infinitely many distinct integers on the card, print on a single line -1.

Otherwise, print on the first line the number of integers that suit you. In the second line, print the numbers in the increasing order. Note that the numbers in the answer can exceed 108 or even be negative (see test samples).

Examples

Input

3
4 1 7


Output

2
-2 10


Input

1
10


Output

-1


Input

4
1 3 5 9


Output

1
7


Input

4
4 3 4 5


Output

0


Input

2
2 4


Output

3
0 3 6
// TO LOVE IS TO KNOW WHAT'S YOUR WORTH. //
// Author :- Saurabh//
//BIT MESRA, RANCHI//
import java.io.*;
import java.util.*;
import static java.lang.Math.*;
public class arithmeticProgression {


    static void Bolo_Jai_Mata_Di() {

        n = ni();

        tsc();      // starting time of execution

        int ar[] = new int[n];
        for (int i = 0; i < n; i++) ar[i] = ni();
        sort(ar, n);
        if (n == 1) {
            pl(-1);
            return;
        }

        TreeMap<Integer, Integer> mp = new TreeMap<>();

        for (int i = 0; i < n - 1; i++) {
            int temp = ar[i + 1] - ar[i];
            if (mp.containsKey(temp)) mp.put(temp, mp.get(temp) + 1);
            else mp.put(temp, 1);
        }
        if (mp.size() == 1) {
            if (mp.firstKey() == 0) {
                pl(1);
                pl(ar[0]);
            } else if (n == 2 && mp.firstKey() % 2 == 0) {
                if (ar[0] == ar[1]) {
                    pl(1);
                    pl(ar[0]);
                } else {
                    pl(3);
                    int d = mp.firstKey();
                    p(ar[0] - d);
                    p(ar[0] + d / 2);
                    p(ar[1] + d);
                }
            } else {
                pl(2);
                int d = mp.firstKey();
                p(ar[0] - d);
                p(ar[n - 1] + d);
            }
        } else if (mp.size() == 2) {
            int d1 = mp.firstKey();
            int d2 = mp.lastKey();
            int x1 = mp.get(d1);
            int x2 = mp.get(d2);
            if (d1 == 0 || d2 == 0) {
                pl(0);
                return;
            } else if (x1 == x2) {
                if (x1 != 1) {
                    pl(0);
                    return;
                }
                pl(1);
                d1 = min(d1, d2);
                for (int i = 1; i < n; i++)
                    if (ar[i] - ar[i - 1] != d1) {
                        pl(ar[i] - d1);
                        break;
                    }
            } else {
                if ((x1 > 1 && x2 != 1) || (x2 > 1 && x1 != 1)) {
                    pl(0);
                    return;
                }
                int flag=0;int temp=-1;
                if (x1 > 1) {
                    for (int i = 1; i < n; i++)
                        if (ar[i] - ar[i - 1] != d1) {
                            temp=(ar[i] - d1);
                            if(temp-ar[i-1]==d1)flag=1;
                            break;
                        }
                } else {
                    for (int i = 1; i < n; i++)
                        if (ar[i] - ar[i - 1] != d2) {
                            temp=(ar[i] - d2);
                            if(temp-ar[i-1]==d2)flag=1;
                            break;
                        }
                }
                if(flag==0){
                    pl(0);
                }
                else {
                    pl(1);
                    pl(temp);
                }
            }

        } else pl(0);


        flush();
    }

    /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
    //THE DON'T CARE ZONE BEGINS HERE...//

    static Calendar ts, te;                                                  //For time calculation
    static int mod9 = 1000000007;
    static int n, m, k, t, mod = 998244353;
    static Lelo input = new Lelo(System.in);
    static PrintWriter pw = new PrintWriter(System.out, true);


    public static void main(String[] args) {      //threading has been used to increase the stack size.

        new Thread(null, null, "BlackRise", 1 << 25)  //the last parameter is stack size desired.,
        {
            public void run() {

                try {
                    Bolo_Jai_Mata_Di();
                    tec();                  //ending time of execution
                    //pwt();                //prints the time taken to execute the program
                } catch (Exception e) {
                    e.printStackTrace();
                    System.exit(1);
                }
            }
        }.start();
    }

    static class Lelo {                                              //Lelo class for fast input
        private InputStream ayega;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;
        private SpaceCharFilter filter;

        public Lelo(InputStream ayega) {
            this.ayega = ayega;
        }

        public int read() {
            if (numChars == -1)
                throw new InputMismatchException();

            if (curChar >= numChars) {
                curChar = 0;
                try {
                    numChars = ayega.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }

                if (numChars <= 0)
                    return -1;
            }
            return buf[curChar++];
        }

        public String nextLine() {
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }

        public int nextInt() {
            int c = read();

            while (isSpaceChar(c))
                c = read();

            int sgn = 1;

            if (c == '-') {
                sgn = -1;
                c = read();
            }

            int res = 0;
            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            }
            while (!isSpaceChar(c));

            return res * sgn;
        }

        public long nextLong() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            long res = 0;

            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            }
            while (!isSpaceChar(c));
            return res * sgn;
        }

        public double nextDouble() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            double res = 0;
            while (!isSpaceChar(c) && c != '.') {
                if (c == 'e' || c == 'E')
                    return res * Math.pow(10, nextInt());
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            }
            if (c == '.') {
                c = read();
                double m = 1;
                while (!isSpaceChar(c)) {
                    if (c == 'e' || c == 'E')
                        return res * Math.pow(10, nextInt());
                    if (c < '0' || c > '9')
                        throw new InputMismatchException();
                    m /= 10;
                    res += (c - '0') * m;
                    c = read();
                }
            }
            return res * sgn;
        }

        public String readString() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = read();
            }
            while (!isSpaceChar(c));

            return res.toString();
        }

        public boolean isSpaceChar(int c) {
            if (filter != null)
                return filter.isSpaceChar(c);
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        public String next() {
            return readString();
        }

        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);
        }
    }

    // functions to take input//
    static int ni() {
        return input.nextInt();
    }

    static long nl() {
        return input.nextLong();
    }

    static double nd() {
        return input.nextDouble();
    }

    static String ns() {
        return input.readString();
    }

    //functions to give output
    static void pl() {
        pw.println();
    }

    static void p(Object o) {
        pw.print(o + " ");
    }

    static void pws(Object o) {
        pw.print(o + "");
    }

    static void pl(Object o) {
        pw.println(o);
    }

    static void tsc()                                          //calculates the starting time of execution
    {
        ts = Calendar.getInstance();
        ts.setTime(new Date());
    }

    static void tec()                                          //calculates the ending time of execution
    {
        te = Calendar.getInstance();
        te.setTime(new Date());
    }

    static void pwt()                                          //prints the time taken for execution
    {
        pw.printf("\nExecution time was :- %f s\n", (te.getTimeInMillis() - ts.getTimeInMillis()) / 1000.00);
    }

    static void flush() {
        pw.flush();
        pw.close();
    }

    static void sort(int ar[], int n) {
        for (int i = 0; i < n; i++) {
            int ran = (int) (Math.random() * n);
            int temp = ar[i];
            ar[i] = ar[ran];
            ar[ran] = temp;
        }
        Arrays.sort(ar);
    }

    static void sort(long ar[], int n) {
        for (int i = 0; i < n; i++) {
            int ran = (int) (Math.random() * n);
            long temp = ar[i];
            ar[i] = ar[ran];
            ar[ran] = temp;
        }
        Arrays.sort(ar);
    }

    static void sort(char ar[], int n) {
        for (int i = 0; i < n; i++) {
            int ran = (int) (Math.random() * n);
            char temp = ar[i];
            ar[i] = ar[ran];
            ar[ran] = temp;
        }
        Arrays.sort(ar);
    }
}