#include <bits/stdc++.h>
#define N 510
using namespace std;
bool query(vector<int> v) {
  cout << "? " << v.size();
  for (auto x : v)
    cout << " " << x;
  cout << '\n';
  cout.flush();
  string s;
  cin >> s;
  return s == "YES";
}
void answer(int x) {
  cout << "! " << x << '\n';
  exit(0);
}
int n, deg[N], a[N], tmp;
vector<int> v[N];
bool dfs(int x, int f, int p) {
  if (x == p)
    return 0;
  bool flag = 1;
  for (auto to : v[x]) {
    if (to == f)
      continue;
    flag &= dfs(to, x, p);
  }
  if (flag)
    tmp = x;
  return flag;
}
int main() {
  cin.tie(0)->sync_with_stdio(0);
  cin >> n;
  for (int i = 1; i < n; i++) {
    int a, b;
    cin >> a >> b, deg[a]++, deg[b]++;
    v[a].push_back(b), v[b].push_back(a);
  }
  for (int i = 1; i <= n; i++)
    a[i] = i;
  sort(a + 1, a + n + 1, [&](int x, int y) { return deg[x] < deg[y]; });
  int l = 2, r = n, ans = -1;
  while (l <= r) {
    int mid = (l + r) >> 1;
    vector<int> v;
    for (int i = 1; i <= mid; i++)
      v.push_back(a[i]);
    if (query(v)) {
      ans = mid, r = mid - 1;
    } else {
      l = mid + 1;
    }
  }
  if (ans == -1)
    answer(a[1]);
  else if (ans != 2)
    answer(a[ans]);
  else {
    int x = a[1], y = a[2];
    dfs(x, x, y);
    if (query({x, tmp}))
      answer(x);
    else
      answer(y);
  }
  return 0;
}