import sys

def main():
    n = int(sys.stdin.readline())
    used = set()
    ans = []
    for _ in range(n):
        u = sys.stdin.readline().strip()
        if len(u) != 3:
            print("Impossible")
            return
        s1 = u[0]
        t1 = u[1:3]
        s2 = u[0:2]
        t2 = u[2]
        valid = False
        if s1 not in used and t1 not in used:
            used.add(s1)
            used.add(t1)
            ans.append(f"{s1} {t1}")
            valid = True
        else:
            if s2 not in used and t2 not in used:
                used.add(s2)
                used.add(t2)
                ans.append(f"{s2} {t2}")
                valid = True
        if not valid:
            print("Impossible")
            return
    print('\n'.join(ans))

if __name__ == "__main__":
    main()