side = input()
n = int(input())
print(n - 2)
if side == 'Alice':
    to = [[] for _ in range(n)]
    for _ in range(n - 1):
        u, v = map(int, input().split())
        u -= 1
        v -= 1
        to[u].append(v)
        to[v].append(u)
    a = []
    for _ in range(n - 2):
        for u in range(n):
            if len(to[u]) != 1:
                continue
            v = to[u][0]
            a.append(v + 1)
            to[u].pop()
            for i in range(len(to[v])):
                if to[v][i] == u:
                    to[v].pop(i)
                    break
            break
    print(*a)
else:
    a = list(map(int, input().split()))
    for i in range(n - 2):
        a[i] -= 1
    cnt = [0] * n
    for x in a: cnt[x] += 1
    done = [False] * n
    for v in a:
        for u in range(n):
            if not done[u] and cnt[u] == 0:
                done[u] = True
                print(u + 1, v + 1)
                break
        cnt[v] -= 1
    i = 0
    while done[i]:
        i += 1
    j = i + 1
    while done[j]:
        j += 1
    print(i + 1, j + 1)