#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int** new_matrix(int height, int width)
{
    int** mx = new int* [height];
    for (int i = 0; i < height; i++)
    {
        mx[i] = new int[width];
    }
    return mx;
}

void reverseStr(string& str)
{
    int n = str.length();
    for (int i = 0; i < n / 2; i++)
    {
        swap(str[i], str[n - i - 1]);
    }
}

int main()
{
    ifstream IN;
    ofstream OUT;
    IN.open("input.txt");

    string str = "";
    getline(IN, str);

    IN.close();

    int n = str.length();

    int** matrix = new_matrix(n, n);

    for (int i = 0; i < n; i++)
    {
        matrix[i][i] = 1;
    }

    int s_j = 1;
    int j = 1;
    int i = 0;
    for (int k = 0; k < n; k++)
    {
        for (i; i < n; i++)
        {
            if (i + 1 == j)
            {
                if (str[i] != str[j])
                {
                    matrix[i][j] = 1;
                }
                else
                {
                    matrix[i][j] = 2;
                }
            }

            else if (i == j)
            {
                matrix[i][j] = 1;
            }

            else if (j > i)
            {
                if (str[i] != str[j])
                {
                    if (matrix[i][j - 1] > matrix[i + 1][j])
                    {
                        matrix[i][j] = matrix[i][j - 1];
                    }
                    else
                    {
                        matrix[i][j] = matrix[i + 1][j];
                    }
                }
                else
                {
                    matrix[i][j] = matrix[i + 1][j - 1] + 2;
                }
            }
            if (j < n - 1)
            {
                j += 1;
            }
        }
        i = 0;
        if (j < n)
        {
            j = s_j + 1;
            s_j = j;
        }
    }

    int length = matrix[0][n - 1];
    i = 0;
    j = n - 1;
    string half_result_string = "";

    while (j >= i)
    {
        if (str[i] == str[j])
        {
            half_result_string += str[i];
            i += 1;
            j -= 1;
        }
        else
        {
            if (matrix[i][j - 1] > matrix[i + 1][j])
            {
                j -= 1;
            }
            else
            {
                i += 1;
            }
        }
    }

    string buffer = "";
    string final_string = "";
    if (length % 2 != 0)
    {
        buffer = half_result_string[length / 2];
        half_result_string = half_result_string.erase(half_result_string.length() - 1, 1);
        final_string += half_result_string;
        final_string += buffer;
        reverseStr(half_result_string);
        final_string += half_result_string;
    }
    else
    {
        final_string += half_result_string;
        reverseStr(half_result_string);
        final_string += half_result_string;
    }

    OUT.open("output.txt");

    OUT << length << "\n";
    for (int i = 0; i < length; i++)
    {
        OUT << final_string[i];
    }

    OUT.close();
}