def main():
    import sys
    input = sys.stdin.read().split()
    n = int(input[0])
    us = input[1:n+1]

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

    for u in us:
        if len(u) != 3:
            possible = False
            break
        # Split options
        s1 = u[0]
        t1 = u[1:3]
        s2 = u[0:2]
        t2 = u[2]

        # Try split1
        if s1 not in used and t1 not in used:
            used.add(s1)
            used.add(t1)
            result.append((s1, t1))
            continue
        # Try split2
        if s2 not in used and t2 not in used:
            used.add(s2)
            used.add(t2)
            result.append((s2, t2))
            continue
        # If neither works
        possible = False
        break

    if not possible:
        print("Impossible")
    else:
        for s, t in result:
            print(f"{s} {t}")

if __name__ == "__main__":
    main()