LPS

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

const int N =  2006;
int dp[N][N];
pair<int,int> bck[N][N]; //  backtracking
string s;

string palindrome(int l, int r){
  if(l == r){
    return string(1, s[l]);
  }
  if(l+1 == r){
    if(s[l] == s[r]){
      return  string(2, s[l]);
    }
    else{
      return "";
    }
  }
  int ll = bck[l][r].first;
  int rr = bck[l][r].second;
  string ret = palindrome(ll, rr);
  if(ll == l+1 and  rr == r-1){
    assert(s[l] == s[r]);
    return string(1,s[l]) + ret + string(1, s[r]);
  }
  return ret;
}

int main () {
    bool done = false;
    while (!done) {

        getline(cin,s);
        if (s == "") {
            done = true;
            break;
        }
        int n = s.size();

        for (int i = 0; i < n; ++i) {
            dp[i][i] = 1;
            bck[i][i] = make_pair(-1, -1);
        }

        for (int len = 2; len <= n; ++len) {
            for (int i = 0; i + len < n + 1; ++i) {
                int j = i + len - 1;

                if (s[i] == s[j] and len == 2) {
                    dp[i][j] = 2;
                    bck[i][j] = make_pair(-1, -1);
                }
                else if (s[i] == s[j]) {
                  bck[i][j] = make_pair(i+1, j-1);
                    dp[i][j] = dp[i+1][j-1] + 2;

                }
                else {
                    if(dp[i+1][j] > dp[i][j-1]){
                      bck[i][j] = make_pair(i+1, j);
                    }else{
                      bck[i][j] = make_pair(i, j-1);
                    }

                    dp[i][j] = max (dp[i + 1][j], dp[i][j - 1]);
                }
            }
        }

        cout << dp[0][n-1] << "\n";
        cout << palindrome(0, n - 1);
    }

    return 0;
}