//CodeForces 412C
1 #include "iostream"
2 #include "cstdio"
3 #include "cstring"
4 #include "algorithm"
5 #include "vector"
6 using namespace std;
7 vector<string> str;
8 int n;
9 string res;
10
11 int main()
12 {
13 int i, j;
14 scanf("%d", &n);
15 str.resize(n + 1);
16 for(i = 1; i <= n; ++i) {
17 cin >> str[i];
18 }
19 int len = str[1].size();
20 for(i = 0; i <= len - 1; ++i) {
21 char c = str[1][i];
22 bool match = 1;
23 for(j = 2; j <= n; ++j) {
24 if(c == '?') {
25 c = str[j][i];
26 }
27 else {
28 if(c == str[j][i] || str[j][i] == '?') {
29 continue;
30 }
31 else {
32 match = 0;
33 break;
34 }
35 }
36 }
37 if(!match)
38 res.push_back('?');
39 else
40 res.push_back(c == '?'? 'x': c);
41 }
42 cout<<res<<endl;
43 }
