func_code_string: #include <bits/stdc++.h>   using namespace std;   long long input() {     long long x = 0, f = 0;     char ch = getchar();     while (ch <  0  || ch >  9 ) f |= ch ==  - , ch = getchar();     while (ch >=  0  && ch <=  9 ) x = x * 10 + ch -  0 , ch = getchar();     return f ? -x : x;   }   const int N = 107;   string s[N];   map<string, int> p;   int vis[N];   string res;   int main() {     int n = input(), m = input();     for (int i = 1; i <= n; i++) {       cin >> s[i];       if (p[s[i]])         res += s[i], vis[i] = vis[p[s[i]]] = 1;       else         reverse(s[i].begin(), s[i].end()), p[s[i]] = i;     }     string ser = res;     reverse(ser.begin(), ser.end());     for (int i = 1; i <= n; i++) {       if (vis[i]) continue;       int flag = 1;       for (int j = 0; j < m / 2; j++) {         if (s[i][j] != s[i][m - j - 1]) {           flag = 0;           break;         }       }       if (flag == 1) {         res += s[i];         break;       }     }     res += ser;     cout << res.length() << endl;     cout << res << endl;   }   