n = int(input())
strings = [input().strip() for _ in range(n)]

used = set()
result = []
possible = True

for u in strings:
    s1 = u[0]
    t1 = u[1:3]
    found = False
    # Check candidate A (1, 2)
    if s1 not in used and t1 not in used:
        used.add(s1)
        used.add(t1)
        result.append(f"{s1} {t1}")
        found = True
    else:
        # Check candidate B (2,1)
        s2 = u[0:2]
        t2 = u[2]
        if s2 not in used and t2 not in used:
            used.add(s2)
            used.add(t2)
            result.append(f"{s2} {t2}")
            found = True
    if not found:
        possible = False
        break

if possible:
    for line in result:
        print(line)
else:
    print("Impossible")