func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     int n, m;     vector<string> a;     vector<string> ra;     cin >> n >> m;     for (int i = 0; i < n; ++i) {       string s;       cin >> s;       a.push_back(s);       reverse(s.begin(), s.end());       ra.push_back(s);     }     vector<int> selected;     vector<int> arr(n, -1);     vector<int> pallindrome;     for (int i = 0; i < n; ++i) {       for (int j = 0; j < n; ++j) {         if (ra[i] == a[j]) {           arr[i] = j;           if (arr[j] != i) {             selected.push_back(i);           } else if (i == j) {             pallindrome.push_back(i);           }         }       }     }     cout << (selected.size() * 2 * m) + (pallindrome.size() > 0 ? 1 : 0) * m          << endl;     for (int i = 0; i < selected.size(); ++i) {       cout << a[selected[i]];     }     if (pallindrome.size() > 0) {       cout << a[pallindrome[0]];     }     for (int i = selected.size() - 1; i >= 0; --i) {       cout << ra[selected[i]];     }     return 0;   }   