#include<bits/stdc++.h>
using namespace std;


int main()
{
    ios_base::sync_with_stdio(0);
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
    string s1, s2;
    cin >> s1;
    for (int i = s1.length() - 1; i >= 0; --i)
    {
        s2 += s1[i];
    }
    int n = s1.length();
    vector< vector <int > > dp(n, vector<int>(n, 0));

    for (int i = 0; i < n; ++i)
    {
        for (int j = 0; j < n; ++j)
        {
            if (s2[i] == s1[j])
            {

                if (j > 0 && i > 0)
                {
                    dp[i][j] = dp[i - 1][j - 1] + 1;
                }
                else
                    dp[i][j] = 1;
            }
            else if (s2[i] != s1[j])
            {
                if (i > 0 && j > 0)
                {
                //cout << i << s1[i] << "  " << j << s2[j] << endl;
                    dp[i][j] = max(dp[i - 1][j], dp[i][j - 1]);
                }
                else if (j <= 0 && i > 0)
                {
                    dp[i][j] = dp[i - 1][j];
                }
                else if (i <= 0 && j > 0)
                {
                    dp[i][j] = dp[i][j - 1];
                }


            }

        }
    }
    for (int i = 0; i < n; ++i)
    {
        for (int j = 0; j < n; ++j)
        {
            cout << dp[i][j] << " " ;
        }
        cout << endl;
    }
    string otv = "";
    dp[0][0] = 0;
    int ii = n - 1, jj = n - 1;
    while (dp[ii][jj] != 0  )
    {
        while (dp[ii][jj] == dp[ii][jj - 1])
        {
            jj--;
            if ( s2[ii] == s1[jj] )
            {
                otv += s2[ii];
                jj--;
                ///cout << s2[ii] << endl;
            }
        }
        if ( s2[ii] == s1[jj] )
            {
                otv += s2[ii];
                jj--;
            }
cerr << " 1 ";
        ii--;
    }
    //cout << dp[3][2] << "   " << s1[3] << s2[2];
    cout << dp[n - 1][n - 1] << endl << otv;
    if (s1[0]==s1[s1.length() - 1]){cout << s1[0];}
}