def read_data():
    N = int(input())
    S= []
    for i in range(N):
        S.append(input().rstrip())
    return N, S

def solve(N, S):
    SENTINEL = chr(ord('z') + 1)
    S = [s + SENTINEL for s in S]
    cursor = [0] * N
    frontiers = [cursor]
    T = []
    while True:
        next_c = SENTINEL
        next_frontiers = []
        for cursor in frontiers:            
            for i, s in enumerate(S):
                c = s[cursor[i]]
                if c < next_c:
                    next_c = c
                    cursor[i] += 1
                    next_frontiers = [cursor[:]]
                    cursor[i] -= 1
                elif c == next_c:
                    cursor[i] += 1
                    next_frontiers.append(cursor[:])
                    cursor[i] -= 1
        if next_c == SENTINEL:
            return T
        T.append(next_c)
        frontiers = next_frontiers


if __name__ == '__main__':
    N, S = read_data()
    minT = solve(N, S)
    print(''.join(minT))