Problem: Alice bought a Congo Prime Video subscription and was watching a documentary on the archaeological findings from Factor's Island on Loch Katrine in Scotland. The archaeologists found a book whose age and origin are unknown. Perhaps Alice can make some sense of it?

The book contains a single string of characters "a", "b" and "c". It has been pointed out that no two consecutive characters are the same. It has also been conjectured that the string contains an unusually long subsequence that reads the same from both sides. 

Help Alice verify this by finding such subsequence that contains at least half of the characters of the original string, rounded down. Note that you don't have to maximise the length of it.

A string a is a subsequence of a string b if a can be obtained from b by deletion of several (possibly, zero or all) characters.

Input

The input consists of a single string s (2 ≤ |s| ≤ 10^6). The string s consists only of characters "a", "b", "c". It is guaranteed that no two consecutive characters are equal.

Output

Output a palindrome t that is a subsequence of s and |t| ≥ ⌊ (|s|)/(2) ⌋.

If there are multiple solutions, you may print any of them. You don't have to maximise the length of t.

If there are no solutions, output a string "IMPOSSIBLE" (quotes for clarity).

Examples

Input


cacbac


Output


aba


Input


abc


Output


a


Input


cbacacacbcbababacbcb


Output


cbaaacbcaaabc

Note

In the first example, other valid answers include "cacac", "caac", "aca" and "ccc". 

Solution (in JAVA):

Solution:



    import java.io.*;
    import java.util.*;
    import java.io.BufferedReader;
    import java.io.IOException;
    import java.util.Collections;
    import java.io.InputStreamReader;
    import static java.lang.Math.*;
    import static java.lang.System.*;

    public class Main1 {




        public static void main(String[] args) throws IOException {

//           try {
           // Scanner in = new Scanner(System.in) ;
             FastScanner in = new FastScanner();
           PrintWriter out = new PrintWriter(System.out);


            char a[] = in.next().toCharArray() ;
            int n = a.length ;
            if (n <=3){
                System.out.println(a[0]);
                return;
            }

            int i=0 , j= n-1 ;
            StringBuilder sb = new StringBuilder();

            while (j-i >=3){
                if (a[i] == a[j]){
                    sb.append(a[i]) ;
                    i++ ;
                    j-- ;
                }
                else if (a[i] == a[j-1]){
                    sb.append(a[i]) ;
                    i++ ;
                    j -=2 ;
                }
                else {
                    sb.append(a[i+1]) ;
                    if (a[i+1] == a[j])j-- ;
                    else if (a[i+1] == a[j-1]) j-=2 ;
                    i += 2 ;

                }

            }
            StringBuilder sb1 = new StringBuilder(sb) ;
            sb1.reverse() ;
           if (i <=j)sb.append(a[i]) ;
            System.out.println(sb + "" + sb1);




            out.flush();
            out.close();

        }
//            catch (Exception e){
//                return;
//            }
//
//        }

        static long gcd(long a, long b) {
            return (b == 0) ? a : gcd(b, a % b);
        }

        static int gcd(int a, int b) {
            return (b == 0) ? a : gcd(b, a % b);
        }

        static void sort(int ar[]) {
            int n = ar.length;
            ArrayList<Integer> a = new ArrayList<>();
            for (int i = 0; i < n; i++)
                a.add(ar[i]);
            Collections.sort(a);
            for (int i = 0; i < n; i++)
                ar[i] = a.get(i);
        }

        static void sort1(long ar[]) {
            int n = ar.length;
            ArrayList<Long> a = new ArrayList<>();
            for (int i = 0; i < n; i++)
                a.add(ar[i]);
            Collections.sort(a);
            for (int i = 0; i < n; i++)
                ar[i] = a.get(i);
        }

        static long ncr(long n, long r, long mod) {
            if (r == 0)
                return 1;
            long val = ncr(n - 1, r - 1, mod);
            val = (n * val) % mod;
            val = (val * modInverse(r, mod)) % mod;
            return val;
        }

        static long fast_pow(long base, long n, long M) {
            if (n == 0)
                return 1;
            if (n == 1)
                return base % M;
            long halfn = fast_pow(base, n / 2, M);
            if (n % 2 == 0)
                return (halfn * halfn) % M;
            else
                return (((halfn * halfn) % M) * base) % M;
        }

        static long modInverse(long n, long M) {
            return fast_pow(n, M - 2, M);
        }

    // ======================================================================================================



        static class FastOutput implements AutoCloseable, Closeable, Appendable {
            private static final int THRESHOLD = 32 << 10;
            private final Writer os;
            private StringBuilder cache = new StringBuilder(THRESHOLD * 2);

            public FastOutput append(CharSequence csq) {
                cache.append(csq);
                return this;
            }

            public FastOutput append(CharSequence csq, int start, int end) {
                cache.append(csq, start, end);
                return this;
            }

            private void afterWrite() {
                if (cache.length() < THRESHOLD) {
                    return;
                }
                flush();
            }

            public FastOutput(Writer os) {
                this.os = os;
            }

            public FastOutput(OutputStream os) {
                this(new OutputStreamWriter(os));
            }

            public FastOutput append(char c) {
                cache.append(c);
                afterWrite();
                return this;
            }

            public FastOutput append(long c) {
                cache.append(c);
                afterWrite();
                return this;
            }

            public FastOutput append(String c) {
                cache.append(c);
                afterWrite();
                return this;
            }

            public FastOutput println() {
                return append(System.lineSeparator());
            }

            public FastOutput flush() {
                try {
                    //            boolean success = false;
                    //            if (stringBuilderValueField != null) {
                    //                try {
                    //                    char[] value = (char[]) stringBuilderValueField.get(cache);
                    //                    os.write(value, 0, cache.length());
                    //                    success = true;
                    //                } catch (Exception e) {
                    //                }
                    //            }
                    //            if (!success) {
                    os.append(cache);
                    //            }
                    os.flush();
                    cache.setLength(0);
                } catch (IOException e) {
                    throw new UncheckedIOException(e);
                }
                return this;
            }

            public void close() {
                flush();
                try {
                    os.close();
                } catch (IOException e) {
                    throw new UncheckedIOException(e);
                }
            }

            public String toString() {
                return cache.toString();
            }

        }


        static class FastScanner {
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            StringTokenizer st = new StringTokenizer("");

            String next() {
                while (!st.hasMoreTokens())
                    try {
                        st = new StringTokenizer(br.readLine());
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                return st.nextToken();
            }

            int nextInt() {
                return Integer.parseInt(next());
            }

            int[] readArray(int n) {
                int[] a = new int[n];
                for (int i = 0; i < n; i++) a[i] = nextInt();
                return a;
            }


            long nextLong() {
                return Long.parseLong(next());
            }
        }


    }