Problem: Fox Ciel is going to publish a paper on FOCS (Foxes Operated Computer Systems, pronounce: "Fox"). She heard a rumor: the authors list on the paper is always sorted in the lexicographical order. 

After checking some examples, she found out that sometimes it wasn't true. On some papers authors' names weren't sorted in lexicographical order in normal sense. But it was always true that after some modification of the order of letters in alphabet, the order of authors becomes lexicographical!

She wants to know, if there exists an order of letters in Latin alphabet such that the names on the paper she is submitting are following in the lexicographical order. If so, you should find out any such order.

Lexicographical order is defined in following way. When we compare s and t, first we find the leftmost position with differing characters: si ≠ ti. If there is no such position (i. e. s is a prefix of t or vice versa) the shortest string is less. Otherwise, we compare characters si and ti according to their order in alphabet.

Input

The first line contains an integer n (1 ≤ n ≤ 100): number of names.

Each of the following n lines contain one string namei (1 ≤ |namei| ≤ 100), the i-th name. Each name contains only lowercase Latin letters. All names are different.

Output

If there exists such order of letters that the given names are sorted lexicographically, output any such order as a permutation of characters 'a'–'z' (i. e. first output the first letter of the modified alphabet, then the second, and so on).

Otherwise output a single word "Impossible" (without quotes).

Examples

Input

3
rivest
shamir
adleman


Output

bcdefghijklmnopqrsatuvwxyz


Input

10
tourist
petr
wjmzbmr
yeputons
vepifanov
scottwu
oooooooooooooooo
subscriber
rowdark
tankengineer


Output

Impossible


Input

10
petr
egor
endagorion
feferivan
ilovetanyaromanova
kostka
dmitriyh
maratsnowbear
bredorjaguarturnik
cgyforever


Output

aghjlnopefikdmbcqrstuvwxyz


Input

7
car
care
careful
carefully
becarefuldontforgetsomething
otherwiseyouwillbehacked
goodluck


Output

acbdefhijklmnogpqrstuvwxyz

Solution (in PYTHON):

Solution:
"""Template for Python Competitive Programmers prepared by Mayank Chaudhary """

# to use the print and division function of Python3
from __future__ import division, print_function

"""value of mod"""
MOD = 998244353
mod = 10**9 + 7

"""use resource"""
# import resource
# resource.setrlimit(resource.RLIMIT_STACK, [0x100000000, resource.RLIM_INFINITY])

"""for factorial"""

# def prepare_factorial():
#     fact = [1]
#     for i in range(1, 100005):
#         fact.append((fact[-1] * i) % mod)
#     ifact = [0] * 100005
#     ifact[100004] = pow(fact[100004], mod - 2, mod)
#     for i in range(100004, 0, -1):
#         ifact[i - 1] = (i * ifact[i]) % mod
#
#     return fact, ifact

"""uncomment next 4 lines while doing recursion based question"""
import threading
threading.stack_size(2**27)
import sys
sys.setrecursionlimit(10000)


"""uncomment modules according to your need"""
# from bisect import bisect_left, bisect_right, insort
# import itertools
# from math import floor, ceil, sqrt
from heapq import heappop, heapify, heappush
# from random import randint as rn
# from Queue import Queue as Q
from collections import Counter, defaultdict

'''
def modinv(n, p):
    return pow(n, p - 2, p)
'''


# def ncr(n, r,  fact, ifact):  # for using this uncomment the lines calculating fact and ifact
#     t = ((fact[n]) * (ifact[r] % mod)) % mod
#     return t



def get_ints(): return map(int, sys.stdin.readline().strip().split())
def get_array(): return list(map(int, sys.stdin.readline().strip().split()))
def input(): return sys.stdin.readline().strip()


# def GCD(x, y):
#     while (y):
#         x, y = y, x % y
#     return x
#
# def lcm(x, y):
#     return (x*y)//(GCD(x, y))
#
# def get_xor(n):
#     return [n,1,n+1,0][n%4]


"""*******************************************************"""

def main():

    def dfs(node, flag):

        if node not in black and mydict[node]:   # means not visited already completely

            grey.add(node)

            for child in mydict[node]:
                if child in grey:       # cycle exist
                    return 1
                flag |= dfs(child, flag)

            grey.remove(node)
            black.add(node)
            return flag
        return 0



    n = int(input())
    Arr = []
    for i in range(n):
        Arr.append(input())
    myset = set()
    mydict = {chr(i) : [] for i in range(97, 123)}
    for i in range(n-1):
        first, second = Arr[i], Arr[i+1]
        length1, length2 = len(first), len(second)
        length = min(length1, length2)
        index = length
        for j in range(length):
            if first[j]!=second[j]:
                mydict[first[j]].append(second[j])
                myset.add((first[j], second[j]))
                index = j
                break

        if first[min(index, length) : ] and not  second[min(index, length):]:
            # print(first, second)
            print('Impossible')
            exit()


    # check if cycle exist in directed graph then answer is impossible
    # if all(not mydict[i] for i in mydict):
    #     print('Impossible')
    #     exit()

    # white = set()
    grey = set()
    black = set()
    flag = 0
    # print(mydict)

    for node in mydict:
        if node not in black:
            flag = dfs(node, flag)
            if flag:
                print('Impossible')
                exit()

    # now we can do the topological sort if there is no cycle

    def DFS(node, stack):

        if node not in myset:
            myset.add(node)

            for child in mydict[node]:
                if child not in myset:
                    DFS(child, stack)

            stack.append(node)


    stack = []
    myset = set()
    # print(mydict)
    for node in mydict:
        if node not in myset and mydict[node]:
            DFS(node, stack)

    # print(stack)

    toposort = stack[::-1]
    # print(toposort)
    check = set(toposort)

    left = [chr(i) for i in range(97, 123) if chr(i) not in check]
    toposort += left

    print(''.join(toposort))









""" -------- Python 2 and 3 footer by Pajenegod and c1729 ---------"""

py2 = round(0.5)
if py2:
    from future_builtins import ascii, filter, hex, map, oct, zip

    range = xrange

import os, sys
from io import IOBase, BytesIO

BUFSIZE = 8192


class FastIO(BytesIO):
    newlines = 0

    def __init__(self, file):
        self._file = file
        self._fd = file.fileno()
        self.writable = "x" in file.mode or "w" in file.mode
        self.write = super(FastIO, self).write if self.writable else None

    def _fill(self):
        s = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
        self.seek((self.tell(), self.seek(0, 2), super(FastIO, self).write(s))[0])
        return s

    def read(self):
        while self._fill(): pass
        return super(FastIO, self).read()

    def readline(self):
        while self.newlines == 0:
            s = self._fill();
            self.newlines = s.count(b"\n") + (not s)
        self.newlines -= 1
        return super(FastIO, self).readline()

    def flush(self):
        if self.writable:
            os.write(self._fd, self.getvalue())
            self.truncate(0), self.seek(0)


class IOWrapper(IOBase):
    def __init__(self, file):
        self.buffer = FastIO(file)
        self.flush = self.buffer.flush
        self.writable = self.buffer.writable
        if py2:
            self.write = self.buffer.write
            self.read = self.buffer.read
            self.readline = self.buffer.readline
        else:
            self.write = lambda s: self.buffer.write(s.encode('ascii'))
            self.read = lambda: self.buffer.read().decode('ascii')
            self.readline = lambda: self.buffer.readline().decode('ascii')


sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)
input = lambda: sys.stdin.readline().rstrip('\r\n')

""" main function"""

if __name__ == '__main__':
    # main()
    threading.Thread(target=main).start()