#!/usr/bin/env python3.8 import sys read = sys.stdin.buffer.read readline = sys.stdin.buffer.readline readlines = sys.stdin.buffer.readlines import itertools import numpy as np from scipy.sparse.csgraph import connected_components N = int(readline()) if N > 52: print('Impossible') exit() words = [readline().rstrip().decode() for _ in range(N)] AB = [] for i, j in itertools.product(range(N), repeat=2): if i == j: continue S = words[i] T = words[j] if S[0] == T[0] or S[1:] == T[1:]: AB.append((2 * i, 2 * j + 1)) if S[-1] == T[-1] or S[:2] == T[:2]: AB.append((2 * i + 1, 2 * j)) if S[0] == T[-1] or S[1:] == T[:2]: AB.append((2 * i, 2 * j)) if S[-1] == T[0] or S[:2] == T[1:]: AB.append((2 * i + 1, 2 * j + 1)) G = np.zeros((N + N, N + N), np.bool) for a, b in AB: G[a, b] = 1 C, comp = connected_components(G, directed=True, connection='strong') graph = [[] for _ in range(C)] in_deg = [0] * C for a, b in AB: ca = comp[a] cb = comp[b] if ca == cb: continue graph[ca].append(cb) in_deg[cb] += 1 order = [] deg_0 = [i for i, x in enumerate(in_deg) if x == 0] while deg_0: v = deg_0.pop() order.append(v) for w in graph[v]: in_deg[w] -= 1 if not in_deg[w]: deg_0.append(w) rank = [0] * C for i, x in enumerate(order): rank[x] = i answers = [] for i in range(N): v = 2 * i w = 2 * i + 1 rv = rank[comp[v]] rw = rank[comp[w]] if rv == rw: print('Impossible') exit() if rv > rw: answers.append((words[i][0], words[i][1:])) else: answers.append((words[i][:2], words[i][2])) for a, b in answers: print(a,b)