#include <bits/stdc++.h>

#ifdef LOCAL
void solve(int N, int L);
int query(int v, int k);
void answer(int x, int y);
namespace {

const int invalid_v_range = 1;
const int invalid_k_range = 2;
const int query_limit_exceeded = 3;
const int invalid_xy_range = 4;
const int no_edge = 5;
const int answer_twice = 6;
const int invalid_answer_times = 7;

int N, L, ok;
std::vector<int> A, B, answered;
std::vector<std::vector<int>> g, dist, que;
std::vector<std::pair<int, int>> p;

int query_count = 0;
int answer_count = 0;

void wronganswer(int code) {
  printf("Wrong Answer [%d]\n", code);
  exit(0);
}

void dfs(int now, int pre, std::vector<std::vector<int>> &g,
         std::vector<int> &dist) {
  for (int nxt : g[now]) {
    if (nxt == pre) {
      continue;
    }
    dist[nxt] = dist[now] + 1;
    dfs(nxt, now, g, dist);
  }
}

}  // namespace

int query(int v, int k) {
  if (v < 1 || N < v) {
    wronganswer(invalid_v_range);
  }
  if (k < 1 || N - 1 < k) {
    wronganswer(invalid_k_range);
  }

  query_count++;
  if (query_count > L) {
    wronganswer(query_limit_exceeded);
  }

  return que[v - 1][k] + 1;
}

void answer(int x, int y) {
  if (x < 1 || N < x || y < 1 || N < y) {
    wronganswer(invalid_xy_range);
  }
  if (x > y) {
    std::swap(x, y);
  }

  answer_count++;
  if (answer_count > N - 1) {
    wronganswer(invalid_answer_times);
  }

  ok = -1;
  for (int i = 0; i < N - 1; i++) {
    if (A[i] == x && B[i] == y) {
      if (answered[i] != 0) {
        wronganswer(answer_twice);
      }
      ok = i;
    }
  }

  if (ok == -1) {
    wronganswer(no_edge);
  }

  answered[ok] = 1;
}

int main(int argc, char **argv) {
  if (scanf("%d", &N) != 1) {
    fprintf(stderr, "Error while reading input.\n");
    exit(1);
  }
  if (scanf("%d", &L) != 1) {
    fprintf(stderr, "Error while reading input.\n");
    exit(1);
  }

  A.resize(N - 1);
  B.resize(N - 1);
  answered.resize(N - 1, 0);
  g.resize(N);
  dist.resize(N, std::vector<int>(N));
  que.resize(N);

  for (int i = 0; i < N - 1; i++) {
    if (scanf("%d", &A[i]) != 1) {
      fprintf(stderr, "Error while reading input.\n");
      exit(1);
    }
    if (scanf("%d", &B[i]) != 1) {
      fprintf(stderr, "Error while reading input.\n");
      exit(1);
    }
  }
  for (int i = 0; i < N - 1; i++) {
    if (A[i] >= B[i]) {
      std::swap(A[i], B[i]);
    }
    g[A[i] - 1].emplace_back(B[i] - 1);
    g[B[i] - 1].emplace_back(A[i] - 1);
  }

  for (int i = 0; i < N; i++) {
    dist[i][i] = 0;
    dfs(i, -1, g, dist[i]);

    p.clear();
    for (int j = 0; j < N; j++) {
      p.emplace_back(dist[i][j], j);
    }
    std::sort(p.begin(), p.end());

    for (int j = 0; j < N; j++) {
      que[i].emplace_back(p[j].second);
    }
  }

  solve(N, L);
  if (answer_count != N - 1) {
    wronganswer(invalid_answer_times);
  }
  printf("Accepted: %d\n", query_count);
  return 0;
}
#else
#include "island.h"
#endif
void solve(int N, int L) {
  const bool sub3 = (2 * N == L);
  const int n = N;
  std::vector<int> ph(n + 1);
  std::vector cc(n + 1, std::vector<bool>(n + 1));
  std::vector<std::pair<int, int>> ans;
  auto unite = [&](int u, int v) {
    cc[u][v] = cc[v][u] = true;
    ans.emplace_back(std::min(u, v), std::max(u, v));
  };
  while (true) {
    int rt = -1;
    for (int i = n; i >= 1; --i) {
      if (ph[i] < 2) {
        rt = i;
        break;
      }
    }
    if (rt == -1) {
      break;
    }
    std::set<int> found;
    for (int i = 1; i < (sub3 ? 3 : n); ++i) {
      int ch = query(rt, i);
      if (ph[ch] > 0 && !cc[ch][rt] && found.contains(ch)) {
        break;
      }
      if (ph[ch] == 2) {
        for (int j = 1; j <= n; ++j) {
          if (cc[ch][j]) {
            found.insert(j);
          }
        }
        continue;
      }
      unite(rt, ch);
      int pre = 0;
      for (int j = 1; j < (sub3 ? 3 : n); ++j) {
        if (pre == rt) {
          break;
        }
        int gch = query(ch, j);
        if (gch == rt) {
          break;
        }
        pre = gch + 1;
        ph[gch] = std::max(1, ph[gch]);
        found.insert(gch);
        unite(ch, gch);
      }
      ph[ch] = 2;
    }
    ph[rt] = 2;
  }
  std::sort(ans.begin(), ans.end());
  ans.erase(std::unique(ans.begin(), ans.end()), ans.end());
  // assert(static_cast<int>(ans.size()) == n - 1);
  for (auto [a, b] : ans) {
    answer(a, b);
  }
}

answer.code:147:10: fatal error: island.h: No such file or directory
  147 | #include "island.h"
      |          ^~~~~~~~~~
compilation terminated.