#include "highway.h"
#include <bits/stdc++.h>
using namespace std;
// macros
typedef long long ll;
typedef long double ld;
typedef pair<int, int> ii;
typedef pair<ll, ll> lll;
typedef tuple<int, int, int> iii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<iii> viii;
typedef vector<ll> vll;
typedef vector<lll> vlll;
#define REP(a,b,c) for(int a=int(b); a<int(c); a++)
#define RE(a,c) REP(a,0,c)
#define RE1(a,c) REP(a,1,c+1)
#define REI(a,b,c) REP(a,b,c+1)
#define REV(a,b,c) for(int a=int(c-1); a>=int(b); a--)
#define FOR(a,b) for(auto& a : b)
#define all(a) a.begin(), a.end()
#define pb push_back
#define popb pop_back
#define fi first
#define se second
const int MX = 2e5;
int n, a, b;
vi U, V;
vi adj[MX];
vi seq, W;
ll normal;
int adjCnt[MX];
void fillAdj() {
RE(i,U.size()) {
adj[U[i]].push_back(i);
adj[V[i]].push_back(i);
}
}
void dfsSeq(int u, int p) {
FOR(e,adj[u]) {
if(V[e] == p || U[e] == p) continue;
if(V[e] == u) swap(V[e], U[e]);
int v = V[e];
seq.push_back(e);
dfsSeq(v, u);
}
}
void findSeqLeaves() {
seq.clear();
queue<int> leaves;
RE(i,n) adjCnt[i] = adj[i].size();
RE(i,n) if(adjCnt[i] == 1) leaves.push(i);
while(!leaves.empty()) {
int u = leaves.front(); leaves.pop();
FOR(e,adj[u]) {
if(V[e] == u) swap(V[e], U[e]);
int v = V[e];
seq.push_back(e);
adjCnt[v]--;
if(adjCnt[v] == 1) leaves.push(v);
}
}
}
int binarySearchSeq() {
int lb=0, ub=n-1;
while(lb != ub) {
int mid=(lb+ub)/2;
W.assign(n-1,0);
REP(i,0,mid+1) W[seq[i]] = 1;
if(ask(W) == normal) lb=mid+1;
else ub=mid;
}
return V[seq[lb]];
}
void findFromS(int S) {
seq.clear();
dfsSeq(S,-1);
reverse(all(seq));
int T = binarySearchSeq();
answer(S,T);
}
void findAnsTree() {
findSeqLeaves();
int S = binarySearchSeq();
findFromS(S);
}
void find_pair(int N, vi _U, vi _V, int A, int B) {
n=N; U=_U; V=_V; a=A; b=B;
fillAdj();
W.assign(n-1,0);
normal = ask(W);
findAnsTree();
}
