#http://bigocoder.com/courses/ONLINE_ORANGE/ONLINE_ORANGE_L01/ORANGE_L01P03/statement

from collections import defaultdict
import string

def dfs (u, graph, visited, result):
    if visited[u] == 1:
        return False
    visited[u] = 1
    if u in graph.keys():
        for v in graph[u]:
            if v in visited:
                if visited[v] != 1:
                    dfs(v, graph, visited, result)
            else:
                result.append(v)
    visited[u] = 2
    result.append(u)

def topologicalSort(graph, result):
    for element in graph.keys():
        if visited[element] == 0:
            if not dfs(element, graph, visited, result):
                return False
    result.reverse()
    return True

def compareTwoString(str1, str2):
    i,j = 0,0
    while i < len(str1) and j < len(str2):
        if str1[i] != str2[j]:
            graph[str1[i]].append(str2[j])
            break
        i+=1
        j+=1
    
number_of_names = int(input())
list_names, result = [], []
graph, visited = defaultdict(list), {}
for i in range(number_of_names):
    list_names.append(str(input()))

for i in range(len(list_names)-1):
    str1, str2 = list_names[i], list_names[i+1]
    if len(str2) < len(str1) and str2.startswith(str1):
        print("Impossible")
        break
    else:
        compareTwoString(str1, str2)

for element in graph.keys():
    visited[element] = 0
print(visited)

isThereNoLoop = topologicalSort(graph, result)
if isThereNoLoop:
    final_result = ''.join(result)
    for element in string.ascii_lowercase:
        if element not in final_result:
            final_result += element
    print(final_result)
else:
    print("Impossible")