from heapq import heappush, heappop
from types import GeneratorType

def bootstrap(f, stack=[]):
    def wrappedfunc(*args, **kwargs):
        if stack:
            return f(*args, **kwargs)
        to = f(*args, **kwargs)
        while True:
            if type(to) is GeneratorType:
                stack.append(to)
                to = next(to)
            else:
                stack.pop()
                if not stack:
                    break
                to = stack[-1].send(to)
        return to
    return wrappedfunc

@bootstrap
def dfs(n, p):
    parent[n] = p
    for v in G[n]:
        if v == p: continue
        cnt[n] += 1
        yield dfs(v, n)
    yield

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

    print(K)

    edge = [list(map(int, input().split())) for _ in range(N-1)]
    G = [[] for _ in range(N)]
    for u, v in edge:
        u, v = u-1, v-1
        G[u].append(v)
        G[v].append(u)
    
    cnt = [0]*N
    parent = [-1]*N
    dfs(0, -1)

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

    ans = []
    for _ in range(N-2):
        n = heappop(que)
        ans.append(parent[n]+1)
        cnt[parent[n]] -= 1
        if cnt[parent[n]] == 0:
            heappush(que, parent[n])

    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)