#include <bits/stdc++.h>
using namespace std;
#define name "code"
#define MAXN 100005
#define pb push_back
#define pf push_front
#define ll long long
#define ii pair<int, int>
#define fs first
#define sc second
#define ill pair<int, ll>
#define lli pair<ll, int>
#define llll pair<ll, ll>
#define all(v) v.begin(),v.end()
#define uni(v) v.erase(unique(all(v)),v.end())
#define bit(n,i) (((n)>>(i))&1)
#define FOR(i,a,b) for (int i=(a),_b=(b); i<=_b; i++)
#define FORD(i,a,b) for (int i=(a),_b=(b); i>=_b; i--)
#define MASK(i) (1LL<<(i))
const int INF=1e9;
const int MOD=1e9+7;
void add(int &u, int v){
u+=v;
if (u>=MOD) u-=MOD;
}
void sub(int &u, int v){
u-=v;
if (u<0) u+=MOD;
}
void minimize(int &u, int v){
u=min(u,v);
}
void maximize(int &u, int v){
u=max(u,v);
}
long long Rand(long long l, long long r){
ll tmp=0;
FOR(i,1,4) tmp=((tmp<<15)^(((1<<15)-1)&rand()));
return l+tmp%(r-l+1);
}
vector<int> adj[MAXN];
const int LOG=17;
int times=0;
int anc[MAXN][LOG+1];
ii cnt[MAXN];
void dfs(int u, int p){
cnt[u].fs=++times;
for (int v:adj[u]){
if (v==p) continue;
anc[v][0]=u;
dfs(v,u);
}
cnt[u].sc=times;
}
bool check_ancestor(int u, int v){
return cnt[u].fs<=cnt[v].fs&&cnt[v].fs<=cnt[u].sc;
}
int lca(int u, int v){
if (check_ancestor(u,v)) return u;
if (check_ancestor(v,u)) return v;
FORD(i,LOG,0)
if (anc[u][i]>=0&&!check_ancestor(anc[u][i],v)) u=anc[u][i];
return anc[u][0];
}
vector<int> label(int n, int k, vector<int> u, vector<int> v){
FOR(i,0,n-2){
adj[u[i]].pb(v[i]);
adj[v[i]].pb(u[i]);
}
memset(anc,-1,sizeof(anc));
dfs(0,-1);
FOR(j,1,LOG) FOR(i,0,n-1) if (anc[i][j-1]!=-1) anc[i][j]=anc[anc[i][j-1]][j-1];
vector<int> kq;
FOR(i,0,n-1) kq.pb(i);
return kq;
}
int find_next_destination(int s, int t, vector<int> c){
if (check_ancestor(s,t)){
return anc[t][0];
}
if (check_ancestor(t,s)){
FORD(j,LOG,0) if (anc[s][j]>=0&&!check_ancestor(anc[s][j],t)) s=anc[s][j];
return s;
}
return anc[t][0];
}
int main()
{
/*
freopen(name".inp","r",stdin);
freopen(name".out","w",stdout);
ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
int n=5,k=10;
vector<int> u={0,1,1,2};
vector<int> v={1,2,3,4};
int s=2,t=0;
vector<int> c={1,4};
label(n,k,u,v);
cout<<find_next_destination(s,t,c);
*/
return 0;
}
