#include <bits/stdc++.h>

using i32 = int32_t;
using ui32 = uint32_t;
using i64 = int64_t;
using ui64 = uint64_t;

using namespace std;

const int N = 101;

int dp[N][N];
pair<int,int> from[N][N];

i32 main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  string s;
  cin >> s;
  const int n = s.size();
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      from[i][j] = pair<int,int>(-1,-1);
    }
  }

  for (int len = 1; len <= n; len++) {
    for (int l = 0; l + len <= n; l++) {
      int r = l + len - 1;
      if (s[l] != s[r]) continue;
      if (len <= 2) {
        dp[l][r] = len;
      } else {
        for (int l1 = l + 1; l1 < r; l1++) {
          for (int r1 = l1; r1 < r; r1++) {
            if (s[l1] == s[r1] && dp[l1][r1] + 1 > dp[l][r]) {
              dp[l][r] = dp[l1][r1] + 2;
              from[l][r] = {l1, r1};
            }
          }
        }
      }
    }
  }

  int mx = 0;
  pair<int,int> ind = {-1,-1};
  for (int l = 0; l < n; l++) {
    for (int r = l; r < n; r++) {
      if (dp[l][r] > mx) {
        ind = {l, r};
        mx = dp[l][r];
      }
    }
  }
  string prefix = "";
  string suffix = "";
  while (ind != pair<int,int>(-1,-1)) {
    if (ind.first == ind.second) {
      prefix.push_back(s[ind.first]);
      ind = from[ind.first][ind.second];
    } else {
      prefix.push_back(s[ind.first]);
      suffix.push_back(s[ind.second]);
      ind = from[ind.first][ind.second];
    }
  }
  reverse(suffix.begin(), suffix.end());
  string answer = prefix + suffix;
  cout << answer.size() << endl;
  cout << answer << endl;
  return 0;
}