#pragma GCC optimize("O3")
#include <bits/stdc++.h>
#define ll long long
#define str string
#define pb push_back
#define pf push_front
#define in insert
#define all(v) v.begin(),v.end()
const int sz=500001,INF=1000000000;
using namespace std;
ll n,num1,num2,dist,maxDist,node1,node2,idx,d[sz],parent[sz][21];
vector<ll>nodes;
vector<bool>isSeen,IsSeen;
vector<pair<ll,ll>>ans;
vector<vector<ll>>nums;
void dfs(ll num)
{
isSeen[num]=true;
for(int i=0;i<nums[num].size();i++)
{
if(!isSeen[nums[num][i]])
{
parent[nums[num][i]][0]=num,d[nums[num][i]]=d[num]+1;
dfs(nums[num][i]);
}
}
}
ll lca(ll num1,ll num2)
{
if(d[num1]<d[num2])
{
swap(num1,num2);
}
for(int i=20;i>=0;i--)
{
if(d[num1]-pow(2,i)>=d[num2])
{
num1=parent[num1][i];
}
}
if(num1==num2)
{
return num1;
}
else
{
for(int i=20;i>=0;i--)
{
if(parent[num1][i]!=parent[num2][i])
{
num1=parent[num1][i],num2=parent[num2][i];
}
}
return parent[num1][0];
}
}
void solve()
{
cin>>n;
nums.resize(n+1),isSeen.resize(n+1),IsSeen.resize(n+1);
for(int i=0;i<n-1;i++)
{
cin>>num1>>num2;
nums[num1].pb(num2),nums[num2].pb(num1);
}
dfs(1);
for(int i=1;i<=20;i++)
{
for(int j=1;j<=n;j++)
{
parent[j][i]=parent[parent[j][i-1]][i-1];
}
}
for(int i=1;i<=n;i++)
{
if(nums[i].size()==1)
{
nodes.pb(i);
}
}
for(int i=0;i<nodes.size();i++)
{
if(!IsSeen[i])
{
maxDist=-INF;
for(int j=0;j<nodes.size();j++)
{
if(i!=j && !IsSeen[j])
{
dist=d[nodes[i]]+d[nodes[j]]-2*d[lca(nodes[i],nodes[j])];
if(dist>maxDist)
{
node1=nodes[i],node2=nodes[j],idx=j,maxDist=dist;
}
}
}
ans.pb({min(node1,node2),max(node1,node2)}),IsSeen[i]=true,IsSeen[idx]=true;
}
}
for(int i=0;i<nodes.size();i++)
{
if(!IsSeen[i])
{
maxDist=-INF;
for(int j=0;j<nodes.size();j++)
{
if(i!=j)
{
dist=d[nodes[i]]+d[nodes[j]]-2*d[lca(nodes[i],nodes[j])];
if(dist>maxDist)
{
node1=nodes[i],node2=nodes[j],idx=j,maxDist=dist;
}
}
}
ans.pb({min(node1,node2),max(node1,node2)});
break;
}
}
cout<<ans.size()<<"\n";
for(int i=0;i<ans.size();i++)
{
cout<<ans[i].first<<" "<<ans[i].second<<"\n";
}
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(nullptr),cout.tie(nullptr);
ll t=1;
//cin>>t;
while(t--)
{
solve();
}
}
