S = input()
n = int(int(input()))
print(n-2)
from heapq import *
if S == "Alice":
    node = [[] for _ in range(n)]
    E = [0] * n
    for _ in range(n-1):
        u, v = list(map(lambda x: int(x)-1, input().split()))
        node[u].append(v)
        node[v].append(u)
        E[u] += 1
        E[v] += 1
    hq = []
    for u in range(n):
        if E[u] == 1:
            heappush(hq, u)
    Ans = []
    while hq:
        u = heappop(hq)
        if E[u] != 1: continue
        for v in node[u]:
            if E[v]:
                E[v] -= 1
                E[u] -= 1
                if E[v] == 1:
                    heappush(hq, (v))
                Ans.append(v+1)
    print(*Ans[:-1])
else:
    Ans = list(map(lambda x: int(x)-1, input().split()))
    A = []
    for i in range(n-2):
        X = [1] * n
        for a in A:
            X[a] = 0
        for a in Ans[i:]:
            X[a] = 0
        a = 0
        while not X[a]:
            a += 1
        print(Ans[i]+1, a+1)
        A.append(a)
    X = [1] * n
    for a in A:
        X[a] = 0
    u = 0
    while not X[u]:
        u += 1
    v = u+1
    while not X[v]:
        v += 1
    print(u+1, v+1)