#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vi = vector<int>;
using vll = vector<ll>;
using vvi = vector<vi>;
using vvll = vector<vll>;
using pii = pair<int,int>;
using pll = pair<ll,ll>;
using ui = unsigned int;
using ull = unsigned long long;
using pui = pair<ui,ui>;
using pull = pair<ull,ull>;
using i128 = __int128_t;
template<typename T>
using vc = std::vector<T>;
#define YES cout << "YES\n"
#define NO cout << "NO\n"
#define yes cout << "yes\n"
#define no cout << "no\n"
#define Yes cout << "Yes\n"
#define No cout << "No\n"
template<typename T> void sc(T &x) { cin >> x; }
template<typename T, typename U> void sc(pair<T,U> &p) { sc(p.first), sc(p.second); }
template<typename T> void sc(vector<T> &v) { for (auto &x : v) sc(x); }
template<typename... A> void sc(A&... a) { (sc(a), ...); }
template<typename T> void _pt(const T &x){cout << x;}
template<typename T, typename U> void _pt(const pair<T,U> &p){_pt(p.first); cout << ' '; _pt(p.second);}
template<typename T> void _pt(const vector<T> &v){bool f=1; for(auto &x:v){if(!f) cout<<' '; _pt(x); f=0;}}
template<typename... A> void pt(const A&... a){(_pt(a), ...);}
template<typename T, typename U> bool umin(T &a, const U &b) { return b < a ? (a = b, true) : false; }
template<typename T, typename U> bool umax(T &a, const U &b) { return b > a ? (a = b, true) : false; }
template<typename T> T maxel(const vector<T>& v){ return *max_element(v.begin(), v.end()); }
template<typename T> T minel(const vector<T>& v){ return *min_element(v.begin(), v.end()); }
template<typename T, int N> T maxel(T (&a)[N]) { return *max_element(a, a + N); }
template<typename T, int N> T minel(T (&a)[N]) { return *min_element(a, a + N); }
template<typename C, typename T> auto lb(C& c, const T& x){ return std::lower_bound(c.begin(), c.end(), x); }
template<typename C, typename T> auto ub(C& c, const T& x){ return std::upper_bound(c.begin(), c.end(), x); }
template<typename T> auto lb(std::set<T>& s, const T& x){ return s.lower_bound(x); }
template<typename T> auto ub(std::set<T>& s, const T& x){ return s.upper_bound(x); }
template<typename T> auto lb(const std::set<T>& s, const T& x){ return s.lower_bound(x); }
template<typename T> auto ub(const std::set<T>& s, const T& x){ return s.upper_bound(x); }
#define GET_MACRO(_1,_2,_3,_4,NAME,...) NAME
#define FOR1(n) for (int i=0; i<(n); ++i)
#define FOR2(i,n) for (int i=0; i<(n); ++i)
#define FOR3(i,l,r) for (int i=(l); i<(r); ++i)
#define FOR4(i,l,r,k) for (int i=(l); i<(r); i+=(k))
#define FOR(...) GET_MACRO(__VA_ARGS__, FOR4, FOR3, FOR2, FOR1)(__VA_ARGS__)
#define ROF1(n) for (int i=(n)-1; i>=0; --i)
#define ROF2(i,n) for (int i=(n)-1; i>=0; --i)
#define ROF3(i,l,r) for (int i=(r)-1; i>=(l); --i)
#define ROF4(i,l,r,k) for (int i=(r)-1; i>=(l); i-=(k))
#define ROF(...) GET_MACRO(__VA_ARGS__, ROF4, ROF3, ROF2, ROF1)(__VA_ARGS__)
#define all(c) (c).begin(), (c).end()
#define allr(c) (c).rbegin(), (c).rend()
#define eb emplace_back
#define mp make_pair
#define mt make_tuple
#define fi first
#define se second
#define pb push_back
#define trav(x,a) for (auto &x : (a))
#define sz(a) ((int)(a).size())
#define mem(a,v) memset(a, v, sizeof(a))
#define nl pt("\n")
vi deg;
int readG(int n, int m) {
vvi _g(n);
FOR(m) {
int _u, _v;
sc(_u, _v);
_u--; _v--;
// _g[_u].pb(_v);
// _g[_v].pb(_u);
deg[_u]++; deg[_v]++;
}
return 1;
}
int32_t main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n;
sc(n);
deg.resize(n);
readG(n, n - 1);
vi list;
FOR(n)
if(deg[i] == 1)
list.pb(i + 1);
int L = sz(list);
pt((L + 1) / 2); nl;
FOR((L + 1) / 2) {
pt(list[i], " ", list[i + L / 2]); nl;
}
// if(L & 1) {
// pt(list[0], " ", list.back()); nl;
// }
return 0;
}
