#include <bits/stdc++.h>
using namespace std;
using ll=long long;
const ll ILL=2167167167167167167;
const int INF=2100000000;
#define rep(i,a,b) for (int i=(int)(a);i<(int)(b);i++)
#define all(p) p.begin(),p.end()
template<class T> using pq_ = priority_queue<T, vector<T>, greater<T>>;
template<class T> int LB(vector<T> &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> int UB(vector<T> &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> bool chmin(T &a,T b){if(b<a){a=b;return 1;}else return 0;}
template<class T> bool chmax(T &a,T b){if(a<b){a=b;return 1;}else return 0;}
template<class T> void So(vector<T> &v) {sort(v.begin(),v.end());}
template<class T> void Sore(vector<T> &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});}
bool yneos(bool a,bool upp=false){if(a){cout<<(upp?"YES\n":"Yes\n");}else{cout<<(upp?"NO\n":"No\n");}return a;}
template<class T> void vec_out(vector<T> &p,int ty=0){
    if(ty==2){cout<<'{';for(int i=0;i<(int)p.size();i++){if(i){cout<<",";}cout<<'"'<<p[i]<<'"';}cout<<"}\n";}
    else{if(ty==1){cout<<p.size()<<"\n";}for(int i=0;i<(int)(p.size());i++){if(i) cout<<" ";cout<<p[i];}cout<<"\n";}}
template<class T> T vec_min(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmin(ans,x);return ans;}
template<class T> T vec_max(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmax(ans,x);return ans;}
template<class T> T vec_sum(vector<T> &a){T ans=T(0);for(auto &x:a) ans+=x;return ans;}
int pop_count(long long a){int res=0;while(a){res+=(int)(a&1),a>>=1;}return res;}
template<class T> T square(T a){return a * a;}



void solve();
// DEAR MYSTERIES / TOMOO
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int t = 1;
    // cin >> t;
    rep(i, 0, t) solve();
}

void solve(){
    string S;
    cin >> S;
    int N;
    cin >> N;
    cout << N - 2 << endl;
    if (S == "Alice") {
        vector<vector<int>> G(N);
        vector<int> to(N);
        rep(i, 0, N - 1) {
            int a, b;
            cin >> a >> b;
            a--, b--;
            G[a].push_back(b);
            G[b].push_back(a);
            to[a]++, to[b]++;
        }
        vector<int> A;
        priority_queue<int> pq;
        rep(i, 0, N) if (to[i] == 1) pq.push(i);
        rep(i, 0, N - 2) {
            int x = pq.top();
            pq.pop();
            to[x] = 0;
            for (auto y : G[x]) if (to[y]) {
                A.push_back(y + 1);
                to[y]--;
                if (to[y] == 1) pq.push(y);
            }
        }
        rep(i, 0, N - 2) {
            if (i) cout << " ";
            cout << A[i];
        }
        cout << endl;
    }
    else {
        vector<int> A(N - 2);
        rep(i, 0, N - 2) cin >> A[i], A[i]--;
        vector<int> las(N, -1);
        rep(i, 0, N - 2) {
            las[A[i]] = i;
        }
        priority_queue<int> pq;
        rep(i, 0, N) if (las[i] == -1) pq.push(i);
        rep(i, 0, N - 2) {
            cout << A[i] + 1 << " " << pq.top() + 1 << endl;
            pq.pop();
            if (las[A[i]] == i) pq.push(A[i]);
        }
        cout << pq.top() + 1 << " ";
        pq.pop();
        cout << pq.top() + 1 << endl;
    }
}