#include "bits/stdc++.h"
#include "highway.h"
#define ll long long
#define all(v) v.begin() , v.end()
#define sz(a) (ll)a.size()
using namespace std;
const ll N = 2e5 + 5;
vector<ll> v[N],Xor,depth[N];
vector<int> Res;
ll n,m,A,B,Dist,vis[N],par[N],sub[N];
inline ll oth(ll c,ll u) {return Xor[c] ^ u;}
void upd(ll c,ll d){
sub[c]=1;
depth[d].push_back(c);
for(ll ind:v[c]){
ll x = oth(ind,c);
if(ind==par[c] || vis[x]) continue;
par[x]=ind;
upd(x,d+1);
sub[c]+=sub[x];
}
}
ll we_know_root(ll rt){
for(ll i=0;i<N;i++) depth[i].clear();
par[rt]=-1;
upd(rt,0);
ll l = 0 , r = sz(depth[Dist]) - 1;
while(l<r){
ll mid = (l+r)/2;
Res.assign(m,0);
for(ll i=0;i<=mid;i++){
ll cur = depth[Dist][i];
while(cur != rt){
Res[par[cur]]=1;
cur = oth(par[cur], cur);
}
}
if(ask(Res)==Dist*B) r=mid;
else l=mid+1;
}
return depth[Dist][l];
}
void find_pair(int _n, vector<int> U, vector<int> V, int _A, int _B){
A=_A,B=_B;
m = sz(U),n = _n;
for(ll i=0;i<m;i++){
Xor.push_back(U[i]^V[i]);
v[U[i]].push_back(i);
v[V[i]].push_back(i);
}
Res.assign(m,0);
Dist = ask(Res) / A;
answer(0, (int) we_know_root(0));
}
