func_code_string: #include <bits/stdc++.h>   using namespace std;   vector<string> mas;   int n, m;   void input() {     cin >> n >> m;     mas.clear();     mas.resize(n);     for (int i = 0; i < n; ++i) cin >> mas[i];   }   void solve() {     string ans = mas[0];     for (int i = 0; i < m; ++i) {       char save = ans[i];       for (char d =  a ; d <=  z ; d++) {         ans[i] = d;         bool f = 1;         for (int j = 0; j < n; ++j) {           int err = 0;           for (int c = 0; c < m; ++c) {             if (ans[c] != mas[j][c]) err++;           }           if (err > 1) {             f = 0;             break;           }         }         if (f) {           cout << ans <<   n ;           return;         }       }       ans[i] = save;     }     cout <<  -1 n ;   }   int main() {     int Q;     cin >> Q;     while (Q--) {       input();       solve();     }     return 0;   }   