Player = input()

N = int(input())
print(N - 2)

if Player == "Alice":
	G = [set() for i in range(N)]
	for _ in range(N - 1):
		u, v = map(int, input().split()); u -= 1; v -= 1
		G[u].add(v)
		G[v].add(u)
	
	A = [0] * (N - 2)
	for i in range(N - 2):
		for v in range(N):
			if len(G[v]) != 1:
				continue
			
			A[i] = list(G[v])[0]
			G[A[i]].remove(v)
			G[v].remove(A[i])
			break
	
	print(*[x + 1 for x in A])

else:
	A = [int(x) - 1 for x in input().split()]
	
	deg = [1] * N
	for a in A:
		deg[a] += 1
	
	ans = []
	for a in A:
		for v in range(N):
			if deg[v] != 1:
				continue
			
			ans.append((a, v))
			deg[a] -= 1
			deg[v] -= 1
			break
	
	last = [i for i in range(N) if deg[i]]
	ans.append((last[0], last[1]))
	
	for u, v in ans:
		print(u + 1, v + 1)