Problem:
Score : 300 points

Problem Statement

There is a box containing N balls. The i-th ball has the integer A_i written on it.
Snuke can perform the following operation any number of times:

Take out two balls from the box. Then, return them to the box along with a new ball, on which the absolute difference of the integers written on the two balls is written.

Determine whether it is possible for Snuke to reach the state where the box contains a ball on which the integer K is written.

Constraints

1 \leq N \leq 10^5

1 \leq A_i \leq 10^9

1 \leq K \leq 10^9

All input values are integers.

Input

Input is given from Standard Input in the following format:

N K
A_1 A_2 ... A_N

Output

If it is possible for Snuke to reach the state where the box contains a ball on which the integer K is written, print POSSIBLE; if it is not possible, print IMPOSSIBLE.

Sample Input 1

3 7
9 3 4

Sample Output 1

POSSIBLE

First, take out the two balls 9 and 4, and return them back along with a new ball, abs(9-4)=5.
Next, take out 3 and 5, and return them back along with abs(3-5)=2.
Finally, take out 9 and 2, and return them back along with abs(9-2)=7.
Now we have 7 in the box, and the answer is therefore POSSIBLE.

Sample Input 2

3 5
6 9 3

Sample Output 2

IMPOSSIBLE

No matter what we do, it is not possible to have 5 in the box. The answer is therefore IMPOSSIBLE.

Sample Input 3

4 11
11 3 7 15

Sample Output 3

POSSIBLE

The box already contains 11 before we do anything. The answer is therefore POSSIBLE.

Sample Input 4

5 12
10 2 8 6 4

Sample Output 4

IMPOSSIBLE

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Linq;
using CompLib.Mathematics;
using CompLib.Util;

public class Program
{
    public void Solve()
    {
        var sc = new Scanner();
        int n = sc.NextInt();
        int k = sc.NextInt();

        long[] a = sc.LongArray();
        var gcd = 0L;
        foreach (long l in a)
        {
            gcd = MathEx.GCD(gcd, l);
        }

        long max = a.Max();

        if (k <= max && (max - k) % gcd == 0)
        {
            Console.WriteLine("POSSIBLE");
        }
        else
        {
            Console.WriteLine("IMPOSSIBLE");
        }
    }

    public static void Main(string[] args) => new Program().Solve();
}

// https://bitbucket.org/camypaper/complib
namespace CompLib.Mathematics
{
    using System;
    using System.Collections.Generic;

    #region GCD LCM

    /// <summary>
    /// 様々な数学的関数の静的メソッドを提供します．
    /// </summary>
    public static partial class MathEx
    {
        /// <summary>
        /// 2 つの整数の最大公約数を求めます．
        /// </summary>
        /// <param name="n">最初の値</param>
        /// <param name="m">2 番目の値</param>
        /// <returns>2 つの整数の最大公約数</returns>
        /// <remarks>ユークリッドの互除法に基づき最悪計算量 O(log N) で実行されます．</remarks>
        public static int GCD(int n, int m)
        {
            return (int) GCD((long) n, m);
        }


        /// <summary>
        /// 2 つの整数の最大公約数を求めます．
        /// </summary>
        /// <param name="n">最初の値</param>
        /// <param name="m">2 番目の値</param>
        /// <returns>2 つの整数の最大公約数</returns>
        /// <remarks>ユークリッドの互除法に基づき最悪計算量 O(log N) で実行されます．</remarks>
        public static long GCD(long n, long m)
        {
            n = Math.Abs(n);
            m = Math.Abs(m);
            while (n != 0)
            {
                m %= n;
                if (m == 0) return n;
                n %= m;
            }

            return m;
        }


        /// <summary>
        /// 2 つの整数の最小公倍数を求めます．
        /// </summary>
        /// <param name="n">最初の値</param>
        /// <param name="m">2 番目の値</param>
        /// <returns>2 つの整数の最小公倍数</returns>
        /// <remarks>最悪計算量 O(log N) で実行されます．</remarks>
        public static long LCM(long n, long m)
        {
            return (n / GCD(n, m)) * m;
        }
    }

    #endregion

    #region PrimeSieve

    public static partial class MathEx
    {
        /// <summary>
        /// ある値までに素数表を構築します．
        /// </summary>
        /// <param name="max">最大の値</param>
        /// <param name="primes">素数のみを入れた数列が返される</param>
        /// <returns>0 から max までの素数表</returns>
        /// <remarks>エラトステネスの篩に基づき，最悪計算量 O(N loglog N) で実行されます．</remarks>
        public static bool[] Sieve(int max, List<int> primes = null)
        {
            var isPrime = new bool[max + 1];
            for (int i = 2; i < isPrime.Length; i++) isPrime[i] = true;
            for (int i = 2; i * i <= max; i++)
                if (!isPrime[i]) continue;
                else
                    for (int j = i * i; j <= max; j += i)
                        isPrime[j] = false;
            if (primes != null)
                for (int i = 0; i <= max; i++)
                    if (isPrime[i])
                        primes.Add(i);

            return isPrime;
        }
    }

    #endregion
}

namespace CompLib.Util
{
    using System;
    using System.Linq;

    class Scanner
    {
        private string[] _line;
        private int _index;
        private const char Separator = ' ';

        public Scanner()
        {
            _line = new string[0];
            _index = 0;
        }

        public string Next()
        {
            while (_index >= _line.Length)
            {
                _line = Console.ReadLine().Split(Separator);
                _index = 0;
            }

            return _line[_index++];
        }

        public int NextInt() => int.Parse(Next());
        public long NextLong() => long.Parse(Next());
        public double NextDouble() => double.Parse(Next());
        public decimal NextDecimal() => decimal.Parse(Next());
        public char NextChar() => Next()[0];
        public char[] NextCharArray() => Next().ToCharArray();

        public string[] Array()
        {
            _line = Console.ReadLine().Split(Separator);
            _index = _line.Length;
            return _line;
        }

        public int[] IntArray() => Array().Select(int.Parse).ToArray();
        public long[] LongArray() => Array().Select(long.Parse).ToArray();
        public double[] DoubleArray() => Array().Select(double.Parse).ToArray();
        public decimal[] DecimalArray() => Array().Select(decimal.Parse).ToArray();
    }
}