from heapq import heappush, heappop

if input() == "Alice":
    N = int(input())
    K = N-2

    print(K)

    edge = [list(map(int, input().split())) for _ in range(N-1)]
    G = [set() for _ in range(N)]
    for u, v in edge:
        u, v = u-1, v-1
        G[u].add(v)
        G[v].add(u)
    
    que = []
    for i in range(N):
        if len(G[i]) == 1:
            heappush(que, i)

    ans = []
    for _ in range(N-2):
        n = heappop(que)
        v = G[n].pop()
        ans.append(v+1)
        G[v].remove(n)
        if len(G[v]) == 1:
            heappush(que, v)

    print(*ans)
else:
    N = int(input())
    K = N-2

    print(K)

    A = list(map(int, input().split()))
    A = [a-1 for a in A]

    cnt = [0]*N
    for a in A:
        cnt[a] += 1

    que = []
    for i in range(N):
        if cnt[i] == 0:
            heappush(que, i)

    edge = []
    for a in A:
        b = heappop(que)
        edge.append((a, b))
        cnt[a] -= 1
        if cnt[a] == 0:
            heappush(que, a)
    l = heappop(que)
    r = heappop(que)
    edge.append((l, r))

    for u, v in edge:
        print(u+1, v+1)