n = int(input())

words = [input() for _ in range(n)]
fst = [w[0] for w in words]
hsh = {f: set([word for word in words if word.startswith(f)]) for f in fst }

while any(len(v) > 1 for v in hsh.values()):
    _hsh = {}
    for k, v in hsh.items():
        if len(v) > 1:
            fs = set([w[len(k)] for w in v if len(k) < len(w)])
            for f in fs:
                pref = k + f
                _hsh[pref] = set([word for word in words if word.startswith(pref)])
            gs = set([w for w in v if len(k) == len(w)])
            if len(gs) > 0:
                _hsh[k] = gs
        else:
            _hsh[k] = v
    hsh= _hsh
print(hsh)