#include<bits/stdc++.h>
using namespace std;
typedef long long int ll;
const int MAXN = 5e5+10;
int n, st[MAXN], tim = 0, r = -1, lfc = 0, par[MAXN];
vector <int> adj[MAXN], tof;
vector <pair<int,int>> ans;
bool dead[MAXN];
void dfs(int v, int parv){
st[v] = tim++;
if((int)adj[v].size()==1) ans.push_back({st[v],v});
for(int u: adj[v])
if(u!=parv && !dead[u]) dfs(u,v);
return;
}
void dfs1(int v, int parv){
for(int u: adj[v])
if(u != parv){
par[u] = v;
dfs1(u,v);
}
return;
}
int main()
{
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
cin >> n;
for(int i = 0; i < n-1; i++){
int u,v;
cin >> u >> v; u--; v--;
adj[v].push_back(u);
adj[u].push_back(v);
}
for(int i = 0; i < n; i++)
if((int)adj[i].size()==1) tof.push_back(i);
if(tof.size()==2){
cout << 1 << '\n' << tof[0]+1 << " " << tof[1]+1 << '\n';
return 0;
}
for(int i = 0; i < n; i++)
if((int)adj[i].size()>=3) r = i;
par[r] = -1;
dfs1(r,-1);
lfc = ((int)tof.size()+1)/2;
cout << lfc << '\n';
if((int)tof.size()%2==1){
int v = tof.back(), v2 = v; tof.pop_back();
while((int)adj[v].size()<=2){
dead[v] = true; v = par[v];
}
cout << v2+1 << " " << r+1 << '\n';
}
dfs(r,-1);
sort(ans.begin(), ans.end());
lfc = (int)ans.size()/2;
for(int i = 0; i < lfc; i++) cout << ans[i].second+1 << " " << ans[i+lfc].second+1 << '\n';
return 0;
}
