func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     int n, m;     cin >> n >> m;     vector<string> v;     vector<string> res;     for (int i = 0; i < n; i++) {       string s;       cin >> s;       v.push_back(s);     }     bool flag = 0;     string t =   , pal =   ;     for (int i = 0; i < v.size(); i++) {       string s = v[i];       t = s;       reverse(s.begin(), s.end());       auto it = find(v.begin(), v.end(), s);       if (it != v.end()) {         if (*it == t) {           flag = 1;           pal = t;           continue;         }         res.push_back(v[i]);         v.erase(it);       }     }     string out =   ;     for (auto x : res) {       out += x;     }     string p = out;     if (flag) out += pal;     reverse(p.begin(), p.end());     out += p;     cout << out.length() <<   n ;     cout << out;   }   