#include <bits/stdc++.h>
using namespace std;

int main() {
	string player; cin >> player;
	int n; cin >> n;
	
	cout << n-2 << endl;
	
	if (player == "Alice") {
		vector<vector<int>> g(n);
		for (int i=0; i<n-1; i++) {
			int x, y; cin >> x >> y; x--; y--;
			g[x].push_back(y);
			g[y].push_back(x);
		}
		
		vector<int> s(n); for (int i=0; i<n; i++) s[i] = g[i].size();
		priority_queue<int, vector<int>, greater<int>> q; for (int i=0; i<n; i++) if (s[i] == 1) q.push(i);
		vector<int> ans;
		for (int i=0; i<n-2; i++) {
			auto x = q.top(); q.pop();
			for (auto& y : g[x]) if (s[y] != 0) {
				ans.push_back(y);
				s[x] = 0; s[y]--;
				if (s[y] == 1) q.push(y);
				break;
			}
		}
		
		for (int i=0; i<n-2; i++) cout << ans[i]+1 << ' ';
		cout << endl;
	} else {
		vector<int> a(n-2), s(n, 1); for (auto& i : a) { cin >> i; i--; }
		for (auto& i : a) s[i]++;
		
		priority_queue<int, vector<int>, greater<int>> q;
		for (int i=0; i<n; i++) if (s[i] == 1) q.push(i);
		
		for (auto& i : a) {
			auto x = q.top(); q.pop();
			cout << x+1 << ' ' << i+1 << endl;
			s[x]--; s[i]--;
			if (s[i] == 1) q.push(i);
		}
		{
			auto x = q.top(); q.pop();
			auto y = q.top(); q.pop();
			cout << y+1 << ' ' << x+1 << endl;
		}
	}
}