#include <iostream>
#include <string>
#include <vector>
using namespace std;
string s;
int v[101][101];
int n;
string pal;

int f(int l, int r)
{
    if (l > r)
        return 0;
    if (v[l][r] != -1)
        return v[l][r];
    if (s[l] == s[r])
        return 2 + f(l+1, r-1);
    return max(f(l+1,r), f(l, r-1));
}

void ans(int l, int r, int pl, int pr)
{
    while (l <= r)
    {
        if (l == r)
        {
            pal[pl] = s[l];
            l++; pl++;
        }
        else
        {
            if (s[l] == s[r])
            {
                pal[pl] = s[l];
                pal[pr] = s[r];
                pl++; pr--; l++; r--;
            }
            else
            {
                if (v[l+1][r] > v[l][r-1])
                    l++;
                else
                    r--;
            }
        }
    }
}

int main()
{
    getline(cin,s);
    n = s.size();
    int res;
    for (int i = 0; i < n; i++)
        for (int j = 0; j < n; j++)
            v[i][j] = -1;
    for (int i = 0; i < n; i++)
        v[i][i] = 1;
    for (int i = 0; i < n; i++)
        for (int j = 0; j < i; j++)
            v[i][j] = -1;
    for (int i = 0; i < n; i++)
        for (int j = 0; j < n; j++)
            v[i][j] = f(i,j);
    v[0][n-1] = f(0,n-1);
    res = v[0][n-1];
    pal = s;
    ans(0,n-1,0,res-1);
    cout << res << endl;
    for (int i = 0; i < res; i++)
        cout << pal[i];
    return 0;
}