//Author: Kevin
#include<bits/stdc++.h>
//#pragma GCC optimize("O2")
using namespace std;
#define ll long long
#define ull unsigned ll
#define pb emplace_back
#define mp make_pair
#define ALL(x) (x).begin(),(x).end()
#define rALL(x) (x).rbegin(),(x).rend()
#define srt(x) sort(ALL(x))
#define rev(x) reverse(ALL(x))
#define rsrt(x) sort(rALL(x))
#define sz(x) (int)(x.size())
#define inf 0x3f3f3f3f
#define pii pair<int,int>
#define lb(v,x) (int)(lower_bound(ALL(v),x)-v.begin())
#define ub(v,x) (int)(upper_bound(ALL(v),x)-v.begin())
#define uni(v) v.resize(unique(ALL(v))-v.begin())
#define longer __int128_t
void die(string S){puts(S.c_str());exit(0);}
vector<int> G[505];
int h[505];
void dfs(int u,int fa)
{
	for(auto v:G[u])
		if(v!=fa)
		{
			dfs(v,u);
			h[u]=max(h[u],h[v]);
		}
	h[u]++;
}
int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	int n;
	cin>>n;
	for(int i=1;i<n;i++)
	{
		int u,v;
		cin>>u>>v;
		G[u].pb(v);
		G[v].pb(u);
	}
	for(int i=1;i<=n;i++)
		if(sz(G[i])>1)
		{
			dfs(i,0);
			break;
		}
	vector<int> vec;
	for(int i=1;i<=n;i++)
		vec.pb(i);
	sort(ALL(vec),[&](int a,int b){return h[a]<h[b]});
	int l=0,r=n-1;
	while(l<r)
	{
		int mid=(l+r)/2;
		vector<int> vq;
		for(int i=0;i<=mid;i++)
			vq.pb(vec[i]);
		cout<<"? "<<sz(vq);
		srt(vq);
		for(auto x:vq)
			cout<<" "<<x;
		cout<<endl;
		string s;
		cin>>s;
		if(s=="YES")
			r=mid;
		else
			l=mid+1;
	}
	cout<<"! "<<vec[l]<<endl;
	return 0;
}

answer.code: In lambda function:
answer.code:57:56: error: expected ‘;’ before ‘}’ token
   57 |         sort(ALL(vec),[&](int a,int b){return h[a]<h[b]});
      |                                                        ^
      |                                                        ;