task5

#include<bits/stdc++.h>

#define endl "\n"
using namespace std;
using ll = long long;
using ld = long double;
using pii = pair<int, int>;

constexpr int N = 1e2 + 5;

string s;
int ans = 0;
int n, id;
int dp[N][N];

int get(int i) {
  fill(&dp[0][0], &dp[N - 1][N], 0);
  string l = s.substr(0, i);
  string r = s.substr(i, n - i);
  reverse(r.begin(), r.end());
  for (int i = 1; i <= l.size(); i++) {
    for (int j = 1; j <= r.size(); j++)
      dp[i][j] = max({dp[i - 1][j - 1] + (l[i - 1] == r[j - 1]), dp[i][j - 1], dp[i - 1][j]});
  }
  return dp[l.size()][r.size()];
}

void Solve() {
  cin >> s;
  n = s.size();
  for (int i = 1; i < n - 1; i++) {
    int v = get(i);
    if (ans < v) {
      ans = v;
      id = i;
    }
  }
  string answer;
  get(id);
  for (int i = id, j = n - id; i && j; ) {
    if (dp[i][j] == dp[i - 1][j])
      i--;
    else if (dp[i][j] == dp[i][j - 1])
      j--;
    else {
      i--;
      j--;
      answer.push_back(s[i]);
    }
  }
  string cp = answer;
  reverse(cp.begin(), cp.end());
  answer = cp + answer;
  cout << answer.size() << endl << answer;
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  // cin >> t;
  // while(t--)
  //auto start = chrono::high_resolution_clock::now();
    Solve();
  //auto end = chrono::high_resolution_clock::now();
  //cout << endl << (chrono::duration_cast<chrono::duration<double>>(end - start)).count();
  return 0;
}