#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define gcd __gcd
#define sz(v) (int) v.size()
#define pb push_back
#define pi pair<int,int>
#define all(v) (v).begin(), (v).end()
#define compact(v) (v).erase(unique(all(v)), (v).end())
#define FOR(i, a, b) for(int i = (a); i <= (b); i++)
#define REV(i, a, b) for(int i = (a); i >= (b); i--)
#define dbg(x) "[" #x " = " << (x) << "]"
///#define int long long
using ll = long long;
using ld = long double;
using ull = unsigned long long;
template<typename T> bool ckmx(T& a, const T& b){if(a < b) return a = b, true; return false;}
template<typename T> bool ckmn(T& a, const T& b){if(a > b) return a = b, true; return false;}
const int N = 2e5+5;
const ll MOD = 1e9+7;
const ll INF = 1e18;
void solve()
{
int n; cin >> n;
vector<vector<int>> adj(n + 1, vector<int>());
for(int i = 1; i < n; i++){
int u,v; cin >> u >> v;
adj[u].pb(v), adj[v].pb(u);
}
vector<int> dp(n + 1, 0);
function<void(int,int)> dfs = [&](int x, int p) -> void{
if(sz(adj[x]) == 1) dp[x] = 1;
for(int v : adj[x])if(v != p){
dfs(v, x);
dp[x] += dp[v];
}
return;
};
vector<int> MnLeaf(n + 1, n + 1);
function<void(int,int)> find_opt = [&](int x, int p) -> void{
for(int v : adj[x])if(v != p){
MnLeaf[v] = min(MnLeaf[v], dp[x] - dp[v]);
find_opt(v, x);
}
for(int v : adj[x])if(v != p){
MnLeaf[x] = min(MnLeaf[x], dp[v]);
}
return;
};
dfs(1, -1); find_opt(1, -1);
int optLeaf = 0;
for(int i = 1; i <= n; i++){
if(MnLeaf[optLeaf] > MnLeaf[i]){
optLeaf = i;
}
}
vector<pair<int,int>> oper; stack<int> save; stack<int> node;
function<void(int,int)> calc_op = [&](int x, int p) -> void{
if(sz(adj[x]) == 1){
if(sz(node)){
oper.push_back(make_pair(node.top(), x));
node.pop();
}
else{
if(x == optLeaf){
node.push(x);
}
else save.push(x);
}
}
for(int v : adj[x])if(v != p){
calc_op(v, x);
if(x == optLeaf){
while(sz(save)){
node.push(save.top());
save.pop();
}
}
}
};
calc_op(1, -1);
if(sz(node)){
oper.push_back(make_pair(node.top(), optLeaf));
node.pop();
}
cout << sz(oper) << "\n";
for(int i = 0; i < sz(oper); i++){
cout << oper[i].first <<" " << oper[i].second << "\n";
}
}
signed main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
#define name "InvMOD"
if(fopen(name".INP", "r")){
freopen(name".INP","r",stdin);
freopen(name".OUT","w",stdout);
}
int t = 1; //cin >> t;
while(t--) solve();
return 0;
}
