#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for(ll i=a;i<b;i++)
#define rrep(i,a,b) for(ll i=a-1;i>=b;i--)
#define ll long long
#define ull unsigned ll
#define ld long double
#define bl __int128_t
#define fi first
#define se second
#define vel vector<ll>
#define vvel vector<vel>
#define pll pair<ll,ll>
#define vepll vector<pll>
#define vvepll vector<vepll>
#define ves vector<string>
#define vem vector<mint>
#define vvem vector<vem>
#define pmm pair<mint,mint>
#define cleout(i) cout<<fixed<<setprecision(i)
template<class T>using PQ=priority_queue<T,vector<T>,greater<T>>;
//               上  右 下 左
vector<int> di={-1, 0, 1, 0};
vector<int> dj={ 0, 1, 0,-1};

vector<int> dx={ 0, 1, 0,-1};
vector<int> dy={ 1, 0,-1, 0};


vector<int> ddx={ 1, 1, 1, 0, -1, -1, -1, 0 };
vector<int> ddy={ 1, 0, -1, -1, -1, 0, 1, 1 };

ll inf=1000000000000000000;//1e18
// LLONG_MAX

mt19937_64 rng((ull)chrono::steady_clock::now().time_since_epoch().count());


void Alice(){
    ll N;
    cin>>N;
    cout<<N-2<<endl;
    vector<set<ll>> G(N);
    vel indeg(N);
    rep(i,0,N-1){
        ll x,y;
        cin>>x>>y;
        x--;
        y--;
        indeg[x]++;
        indeg[y]++;
        G[x].insert(y);
        G[y].insert(x);
    }
    map<ll,set<ll>> ma;
    rep(i,0,N)ma[indeg[i]].insert(i);
    vel a;
    rep(i,0,N-2){
        auto x=*ma[1].begin();
        ma[1].erase(x);
        ll y=*G[x].begin();
        a.push_back(y);
        indeg[x]--;
        ma[indeg[y]].erase(y);
        indeg[y]--;
        G[y].erase(x);
        ma[indeg[y]].insert(y);
    }
    rep(i,0,a.size())cout<<a[i]+1<<" ";
    cout<<endl;
}

void Bob(){
    ll N;
    cin>>N;
    cout<<N-2<<endl;
    vel a(N-2);
    vel deg(N,1);
    rep(i,0,N-2){
        cin>>a[i];
        a[i]--;
        deg[a[i]]++;
    }
    map<ll,set<ll>> ma;
    rep(i,0,N){
        ma[deg[i]].insert(i);
    }
    rep(i,0,N-2){
        ll x=*ma[1].begin();
        ll y=a[i];
        cout<<min(x,y)+1<<" "<<max(x,y)+1<<"\n";
        ma[1].erase(x);
        ma[deg[y]].erase(y);
        deg[x]--;
        deg[y]--;
        ma[deg[y]].insert(y);
    }
    cout<<*ma[1].begin()+1<<" "<<*ma[1].rbegin()+1<<endl;
}


int main(){
    cin.tie(nullptr);
 	ios_base::sync_with_stdio(false);

    
    ll _;
    bool multitest=0;
    if(multitest)cin>>_;
    else _=1;
    string S;
    cin>>S;
    if(S[0]=='A')Alice();
    else Bob();
}