Hv2N8mn1

1#!/usr/bin/env python
2"""(c) gorlum0 [at] gmail.com"""
3import itertools as it
4from sys import stdin
5
6class NetworkXMessageRecovery:
7    def recover(self, messages):
8        res = []
9
10        req = {}
11        for msg in messages:
12            for c in msg:
13                if c not in req: req[c] = set([])
14        for msg in messages:
15            for i, a in enumerate(msg):
16                req[a].update(msg[:i])
17
18        while req:
19            best = min(k for k in req if not req[k])
20            res.append(best)
21            for k in req: req[k].discard(best)
22            del req[best]
23
24        return ''.join(res)
25
26def main():
27    for line in stdin:
28        n = int(line)
29        ## messages = [next(stdin).strip() for _ in xrange(n)]
30        messages = [l.strip() for l in it.islice(stdin, n)]
31
32        print NetworkXMessageRecovery().recover(messages)
33
34if __name__ == '__main__':
35    main()