#include <bits/stdc++.h>

#define fst first
#define snd second
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define clr(a, v) memset( a , v , sizeof(a) )
#define pb push_back
#define mp make_pair
#define sz size()
#define FORN( i , s , n ) for( int64 i = (s) ; i < (n) ; i++ )
#define FOR( i , n ) FORN( i , 0 , n )
#define FORIT( i , x ) for( typeof x.begin() i = x.begin() ; i != x.end() ; i++ )
#define trace(x)    cout << #x << ": " << x << endl;
#define trace2(x, y) cout << #x << ": " << x << " | " << #y << ": " << y << endl;
#define trace3(x, y, z) cerr << #x << ": " << x << " | " << #y << ": " << y << " | " << #z << ": " << z << endl;
#define read ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);

using namespace std;

typedef long long int64;
typedef vector <int64> vi;
typedef pair <int64,int64> ii;
typedef vector <string> vs;
typedef vector <ii> vii;

int N, L; // size of the tree and number of leaves
vi  adj [100005];

int sze [100005]; // number of leaves in the subtree of i
int col [100005]; // color assigned to node i
int maxi[100005]; // maximum number of leaves on a adyacent node of i

vii V;

void dfs(int v, int parent, int color){
    sze[v] = 0; // assign 0
    col[v] = color;// assign color
    maxi[v] = 0;

    FOR(i,adj[v].sz) if ( adj[v][i]!=parent ) {
        dfs(adj[v][i],v,color);
        sze[v]+=sze[adj[v][i]]; //refresh number of leaves
        maxi[v] = max (maxi[v],sze[adj[v][i]]); //refresh maxi
    }
    maxi[v] = max(maxi[v], L-sze[v]); // last refresh for the subtree of the parent
    if (adj[v].sz == 1) {
        sze[v]++; // if v is a leaf add 1
        V.pb(ii(col[v],v+1));
    }
}

int main(){
    int a,b;
    while(cin>>N){
        FOR(i,N) adj[i].clear();//clean the graph
        FOR(i,N-1) {
            cin>>a>>b;a--;b--; // made the tree 0-index
            adj[a].pb(b);
            adj[b].pb(a);
        }
        if (N==2) {cout<<"1\n1 2\n"; continue;}//special case

        L = 0;
        FOR(i,N) if ( adj[i].sz == 1 ) L++; // number of leaves

        // the arrays sze, col and maxi are not cleared because are assigned in each step
        dfs(0,-1,0);// to find the centroid

        int root = -1;
        FOR(i,N) if (adj[i].sz>1 and maxi[i]<=(L/2) ) root = i; // find the centroid

        int  color = 0;

        // assign the color to each  neighbord of the root
        V.clear();
        FOR(i,adj[root].sz) dfs( adj[root][i], root, color++ );

        sort(all(V));
         // vector of leaves
        /*FOR(i,N) if ( adj[i].sz == 1 ) V.pb( ii(col[i],i+1) );
        sort(all(V));// sort by color by special cmp
       */
        // if L%2==1 add the first node
        if (V.sz%2 == 1) V.pb( V[0] );

        cout<<V.sz/2<<endl;
        FOR(i, V.sz/2) cout<< V[i].snd <<" "<<V[i+(V.sz/2)].snd<<endl;

    }
}