Problem p03641 (C++)

Buggy submission (status: Runtime Error):
#pragma region include
#include <iomanip>
#include <iostream>
#include <stdio.h>

#include <algorithm>
#include <cmath>
#include <complex>
#include <sstream>

#include <bitset>
#include <cstring>
#include <string>
#include <tuple>
#include <vector>

#include <complex>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <stack>

#include <fstream>
#include <random>
// #include <time.h>
#include <ctime>
#pragma endregion // #include
/////////
#define REP(i, x, n) for (int i = x; i < n; ++i)
#define rep(i, n) REP(i, 0, n)
#define ALL(X) X.begin(), X.end()
/////////
#pragma region typedef
typedef long long LL;
typedef long double LD;
typedef unsigned long long ULL;
typedef std::pair<LL, LL> PLL;   //
typedef std::pair<int, int> PII; //
#pragma endregion                // typedef
////定数
const int INF = (int)1e9;
const LL MOD = (LL)1e9 + 7;
const LL LINF = (LL)1e18 + 20;
const double PI = acos(-1.0);
const double EPS = 1e-9;
/////////
using namespace ::std;
/////////
#pragma region Math
#pragma region
template <class T> inline T gcd(T a, T b) { return b ? gcd(b, a % b) : a; }
#pragma endregion // 最大公約数 gcd
#pragma region
template <class T> inline T lcm(T a, T b) { return a / gcd(a, b) * b; }
#pragma endregion // 最小公倍数 lcm
#pragma region
LL powMod(LL num, LL n, LL mod = (LL)MOD) { //(num**n)%mod
  num %= mod;                               //
  if (n == 0) {
    return (LL)1;
  }
  LL mul = num;
  LL ans = (LL)1;
  while (n) {
    if (n & 1) {
      ans = (ans * mul) % mod;
    }
    mul = (mul * mul) % mod;
    n >>= 1;
  }
  return ans;
}
LL mod_inverse(LL num, LL mod = MOD) { return powMod(num, MOD - 2, MOD); }
#pragma endregion // 繰り返し二乗法 powMod
#pragma region
template <class T> vector<T> getDivisor(T n) {
  vector<T> v;
  for (int i = 1; i * i <= n; ++i) {
    if (n % i == 0) {
      v.push_back(i);
      if (i != n / i) { // 平方数で重複して数えないように
        v.push_back(n / i);
      }
    }
  }
  sort(v.begin(), v.end());
  return v;
}
#pragma endregion // 約数列挙 getDivisor(n):O(√n)
#pragma endregion // math
// Utility:便利な奴
#pragma region
template <class T> void UNIQUE(vector<T> &vec) {
  sort(vec.begin(), vec.end());
  vec.erase(unique(vec.begin(), vec.end()), vec.end());
}
#pragma endregion // sort erase unique
////////////////////////////////
#pragma region
long long bitcount64(long long bits) {
  bits = (bits & 0x5555555555555555) + (bits >> 1 & 0x5555555555555555);
  bits = (bits & 0x3333333333333333) + (bits >> 2 & 0x3333333333333333);
  bits = (bits & 0x0f0f0f0f0f0f0f0f) + (bits >> 4 & 0x0f0f0f0f0f0f0f0f);
  bits = (bits & 0x00ff00ff00ff00ff) + (bits >> 8 & 0x00ff00ff00ff00ff);
  bits = (bits & 0x0000ffff0000ffff) + (bits >> 16 & 0x0000ffff0000ffff);
  return (bits & 0x00000000ffffffff) + (bits >> 32 & 0x00000000ffffffff);
}
#pragma endregion // その他
////////////////////////////////
struct edge_base {
  int to;
  LL cost;
};
edge_base make_edge_base(int to, LL cost) {
  edge_base ret = {to, cost};
  return ret;
}
#pragma region GRL
#pragma region // グラフ
template <class T, class EDGE>
void dijkstra(int root, int V, vector<T> &dist, vector<vector<EDGE>> G) {
  priority_queue<pair<T, int>, vector<pair<T, int>>, greater<pair<T, int>>> que;
  dist.assign(V, LINF);
  dist[root] = 0;
  que.push(pair<T, int>(0, root)); // 距離、頂点番号

  while (!que.empty()) {
    pair<T, int> p = que.top();
    que.pop();
    int v = p.second;
    if (dist[v] < p.first)
      continue;
    for (int i = 0; i < (int)G[v].size(); ++i) {
      EDGE e = G[v][i];
      if (dist[e.to] > dist[v] + e.cost) {
        dist[e.to] = dist[v] + e.cost;
        que.push(pair<T, int>(dist[e.to], e.to));
      }
    }
  }
}
#pragma endregion // ダイクストラ法:O(|E|log|V|)
#pragma region    // グラフ
void warshall_floyd(vector<vector<LL>> &dist, int V, const LL inf = LINF) {
  for (int k = 0; k < V; ++k) {
    for (int i = 0; i < V; ++i) {
      if (dist[i][k] >= inf)
        continue;
      for (int j = 0; j < V; ++j) {
        if (dist[k][j] >= inf)
          continue;
        dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j]);
      }
    }
  }
}
#pragma endregion // ワーシャルフロイド:O(|V|**3)
#pragma region
namespace FLOW {
// vector< vector<FLOW:edge> > G;

struct edge_flow : public edge_base {
  int cap; // LD cap;//
  int rev;
};
edge_flow make_edge_flow(int to, int cap, int rev, LL cost = 1) {
  // edge_flow make_edge_flow(int to,LD cap,int rev,LL cost=1){
  edge_flow ret;

  ret.to = to;
  ret.cost = cost;
  ret.cap = cap;
  ret.rev = rev;
  return ret;
}

//*
class Graph {
public:
  int V;
  vector<vector<FLOW::edge_flow>> G;
  vector<LL> dist;
  vector<int> iter;
  void init(int v) {
    V = v;
    G.resize(V);
  }
  // directed graph
  void add_edge(int from, int to, int cap) {
    G[from].push_back(FLOW::make_edge_flow(to, cap, G[to].size()));
    G[to].push_back(FLOW::make_edge_flow(from, 0, G[from].size() - 1));
  }

private:
  // sから最短距離をBFSで計算する
  void bfs(int s) { // 許容量もチェックしている
    queue<int> que;
    dist = vector<LL>(V, -1);
    dist[s] = 0;
    que.push(s);
    while (!que.empty()) {
      int v = que.front();
      que.pop();
      for (int i = 0; i < (int)G[v].size(); ++i) {
        edge_flow &e = G[v][i];
        if (e.cap > 0 && dist[e.to] < 0) {
          dist[e.to] = dist[v] + 1;
          que.push(e.to);
        }
      }
    }
  }

private:
  // 増加パスをDFSで探す
  int dfs(int v, int t, int f) {
    if (v == t)
      return f;
    for (int &i = iter[v]; i < (int)G[v].size(); ++i) { //?
      FLOW::edge_flow &e = G[v][i];
      if (e.cap > 0 && dist[v] < dist[e.to]) {
        int d = this->dfs(e.to, t, min(f, e.cap));
        if (d > 0) {
          e.cap -= d;
          G[e.to][e.rev].cap += d;
          return d;
        }
      }
    }
    return 0;
  }

public:
  // sからtへの最大流量を求める
  int max_flow(int s, int t) {
    int flow = 0;
    for (;;) {
      this->bfs(s);
      if (dist[t] < 0)
        return flow;
      iter = vector<int>(V, 0);
      int f;
      while ((f = this->dfs(s, t, INF)) > 0) {
        flow += f;
      }
    }
  }
};
//*/
} // namespace FLOW
#pragma endregion // dinic :O(|E||V|^2)
#pragma region    // グラフ
bool is_bipartite(int v, int c, vector<vector<int>> &G, vector<int> &Color) {
  Color[v] = c;
  for (int i = 0; i < (int)G[v].size(); ++i) { // 隣接グラフ
    if (Color[G[v][i]] == c)
      return false;
    if (Color[G[v][i]] == 0 && !is_bipartite(G[v][i], -c, G, Color)) {
      return false;
    }
  }
  return true;
}
bool is_bipartite(int Root, vector<vector<int>> &Graph) {
  int GraphSize = Graph.size();
  vector<int> Color(GraphSize, 0);
  const int ColorNo = 1;
  return is_bipartite(Root, ColorNo, Graph, Color);
}
#pragma endregion // 二部グラフチェック is_bipartite(root,GraphList)
#pragma endregion //
#pragma region
vector<vector<LL>> NCK; // 初期値:0
// http://sugarknri.hatenablog.com/entry/2016/07/16/165715
void makeinv(vector<LL> &inv, const LL P) {
  int i;
  // const int varMAX = max(100000,(int)inv.size());
  const int varMAX = max(100010, (int)inv.size());

  inv = vector<LL>(varMAX + 1, 0);
  inv[1] = 1;
  for (i = 2; i <= varMAX; i++) {
    inv[i] = (inv[P % i] * (P - P / i) % P) % P; // OVF
    // inv[i] = powMod(i,P-2,P);
  }
}

LL nCk(LL N, LL k, LL mod = MOD) {
  static vector<LL> inv; // modの逆元
  if (inv.size() == 0) {
    makeinv(inv, mod); // modは素数を入れる
  }
  k = min(k, N - k);
  if (k < 0 || k > N) {
    return 0;
  }
  if (k == 0) {
    return 1;
  }
  if (k == 1) {
    return N % mod;
  }
  LL ret = 1;
  for (int i = 1; i <= k; ++i) {
    ret = (ret * ((N + 1 - i) % mod)) % mod; // ret*N:OVF
    ret = (ret * inv[i]) % mod;
  }
  return ret;
}
LL nCk_once(LL N, LL k, LL mod = MOD) { // modは素数
  k = min(k, N - k);
  if (k < 0 || k > N) {
    return 0;
  }
  if (k == 0) {
    return 1;
  }
  if (k == 1) {
    return N % mod;
  }
  LL ret = 1;
  LL A = 1;
  for (LL i = 0; i < k; ++i) {
    A = (A * ((N - i) % mod)) % mod;
  }
  LL B = 1;
  for (LL i = 2; i <= k; ++i) {
    B = (B * (i % mod)) % mod;
  }
  ret = (A * powMod(B, mod - 2, mod)) % mod;
  return ret;
}
#pragma endregion // 組み合わせnCk(,10^5)
#pragma region

LL nCk_base(int N, int K, LL mod = MOD) {
  if (K < 0 || N < K)
    return 0; // 多く取り過ぎ
  K = min(K, N - K);
  if (K == 0) {
    return 1 % mod;
  }
  if (K == 1) {
    return N % mod;
  } //%MOD;
  if (N <= 10000 && NCK[N][K]) {
    return NCK[N][K];
  }
  // N個目を使わない:nCk(N-1,k)
  // N個目を使う	:nCk(N-1,k-1)
  LL ans = (nCk_base(N - 1, K) + nCk_base(N - 1, K - 1)) % mod; //%MOD;
  if (N <= 10000) {
    NCK[N][K] = ans;
  }
  return ans;
}

#pragma endregion // 組み合わせ メモ?
#pragma region CGL
class Point {
public:
  double x, y;
  Point(double x = 0, double y = 0) : x(x), y(y) {}

  Point operator+(Point p) { return Point(add(x, p.x), add(y, p.y)); }
  void operator+=(Point p) {
    x = add(x, p.x);
    y = add(y, p.y);
  }
  Point operator-(Point p) { return Point(add(x, -p.x), add(y, -p.y)); }
  void operator-=(Point p) {
    x = add(x, -p.x);
    y = add(y, -p.y);
  }
  Point operator*(double a) { return Point(x * a, y * a); }
  double operator*(Point p) { return dot(p); }
  Point operator/(double a) { return Point(x / a, y / a); }

  double norm() { return sqrt(x * x + y * y); }
  double dot(Point p) { return add(x * p.x, y * p.y); }
  double rot(Point p) { return add(x * p.y, -y * p.x); }
  double add(double a, double b) {
    double EPS = 1e-10;
    if (abs(a + b) < EPS * (abs(a) + abs(b))) {
      return 0;
    }
    return a + b;
  }
};
istream &operator>>(istream &in, Point &P) {
  in >> P.x >> P.y;
  return in;
}
bool operator==(Point A, Point B) {
  if (A.x == B.x && A.y == B.y)
    return true;
  return false;
}
bool operator<(Point A, Point B) {
  if (A.x < B.x)
    return true;
  else if (A.x > B.x)
    return false;
  if (A.y < B.y)
    return true;
  return false;
}
bool operator>(Point A, Point B) {
  if (A < B)
    return false;
  if (A == B)
    return false;
  return true;
}

// 線分で表した直線の交差判定
bool is_cross(Point p1, Point p2, Point q1, Point q2) {
  double res = (p2 - p1).rot(q2 - q1);
  return res != 0; // 平行なら0
}

/*ccwへ//線分p1-p2上に点qがあるか判定
bool on_seg(Point p1,Point p2,Point q){
        return (p1-q).rot(p2-q) == 0 && (p1-q).dot(p2-q) <= 0;
}*/
// 直線p1-p2と直線q1-q2の交点
// 交差判定をしてから使う:0除算
Point intersection(Point p1, Point p2, Point q1, Point q2) {
  return p1 + (p2 - p1) * ((q2 - q1).rot(q1 - p1) / (q2 - q1).rot(p2 - p1));
}

// 線分ABに対する点C
enum PointPotion {
  ONLINE_BACK = -2,
  CLOCKWISE,
  ON_SEGMENT,
  COUNTER_CLOCKWISE,
  ONLINE_FRONT
};
PointPotion ccw(Point A, Point B, Point C) {
  B -= A;
  C -= A;
  if (B.rot(C) > 0)
    return COUNTER_CLOCKWISE; //+1
  if (B.rot(C) < 0)
    return CLOCKWISE; //-1
  if (B.dot(C) < 0)
    return ONLINE_BACK; //-2
  if (B.norm() < C.norm())
    return ONLINE_FRONT; //+2
  return ON_SEGMENT;     // 0
}
// 線分p1-p2,と線分q1-q2の交差判定
// http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_2_B
bool intersect(Point p1, Point p2, Point q1, Point q2) {
  return (ccw(p1, p2, q1) * ccw(p1, p2, q2) <= 0) &&
         (ccw(q1, q2, p1) * ccw(q1, q2, p2) <= 0);
}
///
// 直線p1-p2と点q1の距離
double dist_LineP(Point p1, Point p2, Point q1) {
  return abs((p2 - p1).rot(q1 - p1)) / (p2 - p1).norm();
}
// 線分p1-p2と点q1の距離
double dist_SegP(Point p1, Point p2, Point q1) {
  //(日)
  if ((p2 - p1).dot(q1 - p1) < 0) {
    return (q1 - p1).norm(); // p1から見てp2と逆方向
  }
  if ((p1 - p2).dot(q1 - p2) < 0) {
    return (q1 - p2).norm(); // p2から見てp1と逆方向
  }
  return dist_LineP(p1, p2, q1); // 垂線下ろす
}
// 線分同士の最短距離
// http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_2_D
// http://judge.u-aizu.ac.jp/onlinejudge/review.jsp?rid=862507#1
double dist_segseg(Point A1, Point A2, Point B1, Point B2) {
  if (intersect(A1, A2, B1, B2)) {
    return 0;
  }
  return min(min(dist_SegP(A1, A2, B1), dist_SegP(A1, A2, B2)),
             min(dist_SegP(B1, B2, A1), dist_SegP(B1, B2, A2)));
}
#pragma endregion // class Point
#pragma region CGL
// 多角形内なら2,線上なら1,外なら0
// http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_3_C
// http://www.prefield.com/algorithm/geometry/contains.html
// 点Pから半直線を引く、ガウス
int contains(vector<Point> &v, Point &P) {
  bool in = false;
  const int N = v.size();
  for (int i = 0; i < N; ++i) {
    Point A = (v[i] - P);
    Point B = (v[(i + 1) % N] - P);
    if (A.y > B.y)
      swap(A, B);
    if (A.y <= 0 && 0 < B.y) {
      if (A.rot(B) < 0)
        in = !in;
    }
    if (A.rot(B) == 0 && A.dot(B) <= 0) {
      return 1; // ON 線上
    }
  }
  return in ? 2 : 0; // 中:外
}
#pragma endregion // contains
#pragma region CGL
// 辞書順で比較
bool cmp_x(const Point &p, const Point &q) {
  if (p.x != q.x)
    return p.x < q.x;
  return p.y < q.y;
}

// 凸包を求める
vector<Point> convex_hull(vector<Point> ps, int n) {
  sort(ps.begin(), ps.end(), cmp_x);
  int k = 0;               // 凸包の頂点数
  vector<Point> qs(n * 2); // 構築中の凸包
  // 下側の凸包の作成
  for (int i = 0; i < n; ++i) {
    while (k > 1 && (qs[k - 1] - qs[k - 2]).rot(ps[i] - qs[k - 1]) <=
                        0) { //<で線上も加える
      k--;
    }
    qs[k++] = ps[i];
  }
  // 上側凸包の作成
  for (int i = n - 2, t = k; i >= 0; i--) {
    while (k > t && (qs[k - 1] - qs[k - 2]).rot(ps[i] - qs[k - 1]) <= 0) { //<
      k--;
    }
    qs[k++] = ps[i];
  }
  qs.resize(k - 1);
  return qs;
}
#pragma endregion // 凸包
#pragma region CGL
double area(vector<Point> poly) {
  int size = poly.size();
  double ans = 0;
  for (int i = 1; i < size - 1; ++i) {
    ans += (poly[i] - poly[0]).rot(poly[i + 1] - poly[0]) / 2;
  }
  return ans;
}
#pragma endregion // 多角形の面積
#pragma region CGL
bool compare_x(Point A, Point B) { return A.x < B.x; }
bool compare_y(Point A, Point B) { return A.y < B.y; }
// vecはx座標の昇順で渡される
double closest_pair(vector<Point>::iterator itr, int N) {
  if (N <= 1)
    return INF;
  int m = N / 2;
  double x = (itr + m)->x;
  double d = min(closest_pair(itr, m), closest_pair((itr + m), N - m));

  inplace_merge(itr, itr + m, itr + N, compare_y);

  vector<Point> B;
  for (int i = 0; i < N; ++i) {
    if (fabs((itr + i)->x - x) >= d)
      continue;
    int Bsize = B.size();
    for (int j = 0; j < Bsize; j++) {
      double dx, dy;
      dx = (itr + i)->x - B[Bsize - j - 1].x;
      dy = (itr + i)->y - B[Bsize - j - 1].y;
      if (dy >= d)
        break;
      d = min(d, hypot(dx, dy));
    }
    B.push_back(*(itr + i));
  }
  return d;
}
#pragma endregion // 最近対 2D
#pragma region CGL
int CircleIntersection(Point A, double AR, Point B, double BR) {
  double D = (B - A).norm();
  if (D > AR + BR) {
    return 4;
  } else if (D == AR + BR) {
    return 3;
  } else if (abs(AR - BR) < D) { //&& D<AR+BR
    return 2;
  } else if (D == abs(AR - BR)) {
    return 1;
  } else if (D + AR < BR || D + BR < AR) {
    return 0;
  }
  return 0; //
}
#pragma endregion // 円と円の位置関係
#pragma region CGL
vector<Point> CircleLine(Point C, double CR, Point A, Point B) {
  vector<Point> ans(2); // 同じ交点なら同じ値
  double a, b, c;
  a = -(A.y - B.y);
  b = A.x - B.x;
  c = -(a * A.x + b * A.y);

  double l, k, d;
  l = a * a + b * b;
  k = a * C.x + b * C.y + c;
  d = l * CR * CR - k * k;
  if (d > 0) {
    double ds = sqrt(d);
    double apl = a / l;
    double bpl = b / l;
    double xc = C.x - apl * k;
    double yc = C.y - bpl * k;
    double xd = bpl * ds;
    double yd = apl * ds;
    Point temp;
    ans[0].x = xc - xd;
    ans[0].y = yc + yd;
    ans[1].x = xc + xd;
    ans[1].y = yc - yd;
  } else if (d == 0) {
    Point temp;
    temp.x = C.x - a * k / l;
    temp.y = C.y - b * k / l;
    ans[0] = temp;
    ans[1] = temp;
  } else {
    Point temp;
    temp.x = INF;
    temp.y = INF;
    ans[0] = temp;
    ans[1] = temp;
  }
  return ans;
}
#pragma endregion // 円と直線の交点,距離チェックする。

#pragma region DSL
class UnionFind {
public:
  int cNum; // 要素数
  vector<int> parent;
  vector<int> count;
  vector<vector<int>> GList;
  UnionFind(int n) {
    cNum = n;
    parent = vector<int>(n);
    count = vector<int>(n, 1);
    GList.resize(n);
    for (int i = 0; i < n; ++i) {
      parent[i] = i;
      GList[i].push_back(i);
    }
  }
  int find(int x) {
    if (parent[x] == x) {
      return x;
    }
    return parent[x] = find(parent[x]);
  }
  bool same(int x, int y) { return find(x) == find(y); }
  int Count(int x) { return count[find(x)]; }
  void add(int x, int y) { // union
    x = find(x);
    y = find(y);
    if (x == y)
      return;
    parent[x] = y;

    count[y] += count[x];
    if (GList[y].size() < GList[x].size()) {
      swap(GList[x], GList[y]);
    }
    GList[y].insert(GList[y].end(), GList[x].begin(), GList[x].end());
  }
};

#pragma endregion // UnionFind
#pragma region DSL
class segment {};
#pragma endregion // segment tree
#pragma region DSL
class BITree { // 1-index
  int N;
  vector<LL> bit;

public:
  BITree(int n) {
    N = n;
    bit = vector<LL>(N + 1, 0); // 1-index
  }
  void add(int a, LL w) { // aにwを足す
    if (a <= 0 || N < a)
      return; // a:[1,N]
    for (int i = a; i <= N; i += i & -i) {
      bit[i] += w;
    }
  }
  LL sum(int a) { //[1,a]の和,a:[1,N]
    /*
    1番目からa番目までの和、1-index
    */
    LL ret = 0;
    if (a > N)
      a = N;
    for (int i = a; i > 0; i -= i & -i) {
      ret += bit[i];
    }
    return ret;
  }
};
#pragma endregion // BIndexTree

#pragma region
template <class T, class U> istream &operator>>(istream &in, pair<T, U> &P) {
  in >> P.first >> P.second;
  return in;
}
#pragma endregion // cin pair<T,U>
#pragma region
template <class T> istream &operator>>(istream &in, vector<T> &v) {
  int size = v.size();
  for (int i = 0; i < size; ++i) {
    in >> v[i];
  }
  return in;
}
#pragma endregion // cin vector<int>
#pragma region
// 行列の積
namespace mymat {
LL matMOD = MOD; // 初期値10^9 + 7
};
template <class T>
vector<vector<T>> operator*(vector<vector<T>> &A, vector<vector<T>> &B) {
  LL mod = mymat::matMOD;
  int R = A.size();
  int cen = A[0].size();
  int C = B[0].size();
  vector<vector<T>> ans(R, vector<T>(C, 0));
  for (int row = 0; row < R; ++row) {
    for (int col = 0; col < C; ++col) {
      for (int inner = 0; inner < cen; ++inner) {
        ans[row][col] = (ans[row][col] + A[row][inner] * B[inner][col]) % mod;
        // ans[row][col] = (ans[row][col] + A[row][inner]*B[inner][col]);
      }
    }
  }
  return ans;
}

template <class T>
vector<vector<T>> powMod(vector<vector<T>> mat, LL N, LL mod = MOD) {
  mymat::matMOD = mod;
  int R = mat.size();
  int C = mat[0].size();
  // R==C
  vector<vector<T>> I(R, vector<T>(C, 0)); // 単位元
  for (int i = 0; i < R && i < C; ++i) {
    I[i][i] = 1;
  }
  if (N == 0) {
    return I;
  }
  vector<vector<T>> mul(R, vector<T>(C)), ans(R, vector<T>(C));
  ans = I;
  mul = mat;
  while (N) {
    if (N & 1) {
      ans = ans * mul;
    }
    N >>= 1;
    mul = mul * mul;
  }
  return ans;
}
#pragma endregion // 行列

#pragma region
namespace TIME {
time_t start, limit;
void time_start() { start = time(NULL); }
void time_set(int num) { limit = num; } // 秒
bool check() { return (time(NULL) - start < limit); }
} // namespace TIME
#pragma endregion // 時間計測

#pragma region
/*
namespace RAND{
mt19937 mt;
void rand_init(){
        random_device rnd;
        mt = mt19937(rnd());
}
int rand(){
        return mt();
}
}
*/
#pragma endregion // 乱数

#pragma region
#pragma endregion //

//////////////////
template <typename T> class segment_base {
  int N; // 要素数
  vector<T> dat1;
  T VAL_E; // 初期値
public:
  segment_base(){};
  segment_base(int n, T val_E) : N(n), VAL_E(val_E) {
    dat1.resize(2 * n);
    dat1.assign(2 * n, val_E); // 初期化
  }
  void init(int n, T val_E) {
    N = n;
    VAL_E = val_E;
    dat1.resize(2 * n);
    dat1.assign(2 * n, val_E);
  }
  T SELECT(T L, T R) { // 扱う演算子
    T ans;
    ans = min(L, R); //
    return ans;
  }

  // index番目の値をvalに変更,indexは"0-index"
  void update(int index, T val) {
    for (dat1[index += N] = val; index > 1; index >>= 1) {
      dat1[index >> 1] = SELECT(dat1[index], dat1[index ^ 1]); // index+0,+1
    }
  }

  // 区間[L,R)のSELECT
  T query(int L, int R) {
    T ans = VAL_E; //
    for (L += N, R += N; L < R; L >>= 1, R >>= 1) {
      if (L & 1)
        ans = SELECT(ans, dat1[L++]);
      if (R & 1)
        ans = SELECT(ans, dat1[--R]);
    }
    return ans;
  }
};
//////////////////
vector<int> A;
vector<int> Aindex;       // Aの値からインデックスをえる。
segment_base<int> seg[2]; // 偶数、奇数0-index

void solve() {
  int N;
  cin >> N;
  A.resize(N);
  Aindex.resize(N + 1);
  seg[0].init(N, INF);
  seg[1].init(N, INF);

  for (int i = 0; i < N; ++i) {
    cin >> A[i];
    Aindex[A[i]] = i;
    seg[i & 1].update(i, A[i]);
  }

  vector<int> start(3);
  start[1] = 0;
  start[2] = N;
  start[0] = seg[start[1] & 1].query(start[1], start[2]);
  priority_queue<vector<int>, vector<vector<int>>, greater<vector<int>>> que;
  que.push(start);
  int pos = 0;
  vector<int> ans(N);
  vector<int> temp(3);
  while (!que.empty()) {
    temp = que.top();
    que.pop();
    int L, R; // 値
    L = temp[0];
    int Lindex = Aindex[L];

    R = seg[(Lindex & 1) ^ 1].query(temp[1], temp[2]);
    int Rindex = Aindex[R];

    ans[pos++] = L;
    ans[pos++] = R;

    // 区間の分割	,取った間は偶奇がずれる。
    vector<int> next(3);
    if (temp[1] < Lindex) {
      next[1] = temp[1];
      next[2] = Lindex;
      next[0] = seg[next[1] & 1].query(next[1], next[2]);
      que.push(next);
    }
    if (Lindex + 1 < Rindex) {
      next[1] = Lindex + 1;
      next[2] = Rindex;
      next[0] = seg[next[1] & 1].query(next[1], next[2]);
      que.push(next);
    }
    if (Rindex + 1 < temp[2]) {
      next[1] = Rindex + 1;
      next[2] = temp[2];
      next[0] = seg[next[1] & 1].query(next[1], next[2]);
      que.push(next);
    }
  }

  for (int i = 0; i < N; ++i) {
    if (i)
      cout << " ";
    cout << ans[i];
  }
  cout << endl;
}

#pragma region main
signed main(void) {
  std::cin.tie(0);
  std::ios::sync_with_stdio(false);
  std::cout << std::fixed; // 小数を10進数表示
  cout << setprecision(16); // 小数点以下の桁数を指定//coutとcerrで別

  solve();
}
#pragma endregion // main()

Fixed submission:
#pragma region include
#include <iomanip>
#include <iostream>
#include <stdio.h>

#include <algorithm>
#include <cmath>
#include <complex>
#include <sstream>

#include <bitset>
#include <cstring>
#include <string>
#include <tuple>
#include <vector>

#include <complex>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <stack>

#include <fstream>
#include <random>
// #include <time.h>
#include <ctime>
#pragma endregion // #include
/////////
#define REP(i, x, n) for (int i = x; i < n; ++i)
#define rep(i, n) REP(i, 0, n)
#define ALL(X) X.begin(), X.end()
/////////
#pragma region typedef
typedef long long LL;
typedef long double LD;
typedef unsigned long long ULL;
typedef std::pair<LL, LL> PLL;   //
typedef std::pair<int, int> PII; //
#pragma endregion                // typedef
////定数
const int INF = (int)1e9;
const LL MOD = (LL)1e9 + 7;
const LL LINF = (LL)1e18 + 20;
const double PI = acos(-1.0);
const double EPS = 1e-9;
/////////
using namespace ::std;
/////////
#pragma region Math
#pragma region
template <class T> inline T gcd(T a, T b) { return b ? gcd(b, a % b) : a; }
#pragma endregion // 最大公約数 gcd
#pragma region
template <class T> inline T lcm(T a, T b) { return a / gcd(a, b) * b; }
#pragma endregion // 最小公倍数 lcm
#pragma region
LL powMod(LL num, LL n, LL mod = (LL)MOD) { //(num**n)%mod
  num %= mod;                               //
  if (n == 0) {
    return (LL)1;
  }
  LL mul = num;
  LL ans = (LL)1;
  while (n) {
    if (n & 1) {
      ans = (ans * mul) % mod;
    }
    mul = (mul * mul) % mod;
    n >>= 1;
  }
  return ans;
}
LL mod_inverse(LL num, LL mod = MOD) { return powMod(num, MOD - 2, MOD); }
#pragma endregion // 繰り返し二乗法 powMod
#pragma region
template <class T> vector<T> getDivisor(T n) {
  vector<T> v;
  for (int i = 1; i * i <= n; ++i) {
    if (n % i == 0) {
      v.push_back(i);
      if (i != n / i) { // 平方数で重複して数えないように
        v.push_back(n / i);
      }
    }
  }
  sort(v.begin(), v.end());
  return v;
}
#pragma endregion // 約数列挙 getDivisor(n):O(√n)
#pragma endregion // math
// Utility:便利な奴
#pragma region
template <class T> void UNIQUE(vector<T> &vec) {
  sort(vec.begin(), vec.end());
  vec.erase(unique(vec.begin(), vec.end()), vec.end());
}
#pragma endregion // sort erase unique
////////////////////////////////
#pragma region
long long bitcount64(long long bits) {
  bits = (bits & 0x5555555555555555) + (bits >> 1 & 0x5555555555555555);
  bits = (bits & 0x3333333333333333) + (bits >> 2 & 0x3333333333333333);
  bits = (bits & 0x0f0f0f0f0f0f0f0f) + (bits >> 4 & 0x0f0f0f0f0f0f0f0f);
  bits = (bits & 0x00ff00ff00ff00ff) + (bits >> 8 & 0x00ff00ff00ff00ff);
  bits = (bits & 0x0000ffff0000ffff) + (bits >> 16 & 0x0000ffff0000ffff);
  return (bits & 0x00000000ffffffff) + (bits >> 32 & 0x00000000ffffffff);
}
#pragma endregion // その他
////////////////////////////////
struct edge_base {
  int to;
  LL cost;
};
edge_base make_edge_base(int to, LL cost) {
  edge_base ret = {to, cost};
  return ret;
}
#pragma region GRL
#pragma region // グラフ
template <class T, class EDGE>
void dijkstra(int root, int V, vector<T> &dist, vector<vector<EDGE>> G) {
  priority_queue<pair<T, int>, vector<pair<T, int>>, greater<pair<T, int>>> que;
  dist.assign(V, LINF);
  dist[root] = 0;
  que.push(pair<T, int>(0, root)); // 距離、頂点番号

  while (!que.empty()) {
    pair<T, int> p = que.top();
    que.pop();
    int v = p.second;
    if (dist[v] < p.first)
      continue;
    for (int i = 0; i < (int)G[v].size(); ++i) {
      EDGE e = G[v][i];
      if (dist[e.to] > dist[v] + e.cost) {
        dist[e.to] = dist[v] + e.cost;
        que.push(pair<T, int>(dist[e.to], e.to));
      }
    }
  }
}
#pragma endregion // ダイクストラ法:O(|E|log|V|)
#pragma region    // グラフ
void warshall_floyd(vector<vector<LL>> &dist, int V, const LL inf = LINF) {
  for (int k = 0; k < V; ++k) {
    for (int i = 0; i < V; ++i) {
      if (dist[i][k] >= inf)
        continue;
      for (int j = 0; j < V; ++j) {
        if (dist[k][j] >= inf)
          continue;
        dist[i][j] = min(dist[i][j], dist[i][k] + dist[k][j]);
      }
    }
  }
}
#pragma endregion // ワーシャルフロイド:O(|V|**3)
#pragma region
namespace FLOW {
// vector< vector<FLOW:edge> > G;

struct edge_flow : public edge_base {
  int cap; // LD cap;//
  int rev;
};
edge_flow make_edge_flow(int to, int cap, int rev, LL cost = 1) {
  // edge_flow make_edge_flow(int to,LD cap,int rev,LL cost=1){
  edge_flow ret;

  ret.to = to;
  ret.cost = cost;
  ret.cap = cap;
  ret.rev = rev;
  return ret;
}

//*
class Graph {
public:
  int V;
  vector<vector<FLOW::edge_flow>> G;
  vector<LL> dist;
  vector<int> iter;
  void init(int v) {
    V = v;
    G.resize(V);
  }
  // directed graph
  void add_edge(int from, int to, int cap) {
    G[from].push_back(FLOW::make_edge_flow(to, cap, G[to].size()));
    G[to].push_back(FLOW::make_edge_flow(from, 0, G[from].size() - 1));
  }

private:
  // sから最短距離をBFSで計算する
  void bfs(int s) { // 許容量もチェックしている
    queue<int> que;
    dist = vector<LL>(V, -1);
    dist[s] = 0;
    que.push(s);
    while (!que.empty()) {
      int v = que.front();
      que.pop();
      for (int i = 0; i < (int)G[v].size(); ++i) {
        edge_flow &e = G[v][i];
        if (e.cap > 0 && dist[e.to] < 0) {
          dist[e.to] = dist[v] + 1;
          que.push(e.to);
        }
      }
    }
  }

private:
  // 増加パスをDFSで探す
  int dfs(int v, int t, int f) {
    if (v == t)
      return f;
    for (int &i = iter[v]; i < (int)G[v].size(); ++i) { //?
      FLOW::edge_flow &e = G[v][i];
      if (e.cap > 0 && dist[v] < dist[e.to]) {
        int d = this->dfs(e.to, t, min(f, e.cap));
        if (d > 0) {
          e.cap -= d;
          G[e.to][e.rev].cap += d;
          return d;
        }
      }
    }
    return 0;
  }

public:
  // sからtへの最大流量を求める
  int max_flow(int s, int t) {
    int flow = 0;
    for (;;) {
      this->bfs(s);
      if (dist[t] < 0)
        return flow;
      iter = vector<int>(V, 0);
      int f;
      while ((f = this->dfs(s, t, INF)) > 0) {
        flow += f;
      }
    }
  }
};
//*/
} // namespace FLOW
#pragma endregion // dinic :O(|E||V|^2)
#pragma region    // グラフ
bool is_bipartite(int v, int c, vector<vector<int>> &G, vector<int> &Color) {
  Color[v] = c;
  for (int i = 0; i < (int)G[v].size(); ++i) { // 隣接グラフ
    if (Color[G[v][i]] == c)
      return false;
    if (Color[G[v][i]] == 0 && !is_bipartite(G[v][i], -c, G, Color)) {
      return false;
    }
  }
  return true;
}
bool is_bipartite(int Root, vector<vector<int>> &Graph) {
  int GraphSize = Graph.size();
  vector<int> Color(GraphSize, 0);
  const int ColorNo = 1;
  return is_bipartite(Root, ColorNo, Graph, Color);
}
#pragma endregion // 二部グラフチェック is_bipartite(root,GraphList)
#pragma endregion //
#pragma region
vector<vector<LL>> NCK; // 初期値:0
// http://sugarknri.hatenablog.com/entry/2016/07/16/165715
void makeinv(vector<LL> &inv, const LL P) {
  int i;
  // const int varMAX = max(100000,(int)inv.size());
  const int varMAX = max(100010, (int)inv.size());

  inv = vector<LL>(varMAX + 1, 0);
  inv[1] = 1;
  for (i = 2; i <= varMAX; i++) {
    inv[i] = (inv[P % i] * (P - P / i) % P) % P; // OVF
    // inv[i] = powMod(i,P-2,P);
  }
}

LL nCk(LL N, LL k, LL mod = MOD) {
  static vector<LL> inv; // modの逆元
  if (inv.size() == 0) {
    makeinv(inv, mod); // modは素数を入れる
  }
  k = min(k, N - k);
  if (k < 0 || k > N) {
    return 0;
  }
  if (k == 0) {
    return 1;
  }
  if (k == 1) {
    return N % mod;
  }
  LL ret = 1;
  for (int i = 1; i <= k; ++i) {
    ret = (ret * ((N + 1 - i) % mod)) % mod; // ret*N:OVF
    ret = (ret * inv[i]) % mod;
  }
  return ret;
}
LL nCk_once(LL N, LL k, LL mod = MOD) { // modは素数
  k = min(k, N - k);
  if (k < 0 || k > N) {
    return 0;
  }
  if (k == 0) {
    return 1;
  }
  if (k == 1) {
    return N % mod;
  }
  LL ret = 1;
  LL A = 1;
  for (LL i = 0; i < k; ++i) {
    A = (A * ((N - i) % mod)) % mod;
  }
  LL B = 1;
  for (LL i = 2; i <= k; ++i) {
    B = (B * (i % mod)) % mod;
  }
  ret = (A * powMod(B, mod - 2, mod)) % mod;
  return ret;
}
#pragma endregion // 組み合わせnCk(,10^5)
#pragma region

LL nCk_base(int N, int K, LL mod = MOD) {
  if (K < 0 || N < K)
    return 0; // 多く取り過ぎ
  K = min(K, N - K);
  if (K == 0) {
    return 1 % mod;
  }
  if (K == 1) {
    return N % mod;
  } //%MOD;
  if (N <= 10000 && NCK[N][K]) {
    return NCK[N][K];
  }
  // N個目を使わない:nCk(N-1,k)
  // N個目を使う	:nCk(N-1,k-1)
  LL ans = (nCk_base(N - 1, K) + nCk_base(N - 1, K - 1)) % mod; //%MOD;
  if (N <= 10000) {
    NCK[N][K] = ans;
  }
  return ans;
}

#pragma endregion // 組み合わせ メモ?
#pragma region CGL
class Point {
public:
  double x, y;
  Point(double x = 0, double y = 0) : x(x), y(y) {}

  Point operator+(Point p) { return Point(add(x, p.x), add(y, p.y)); }
  void operator+=(Point p) {
    x = add(x, p.x);
    y = add(y, p.y);
  }
  Point operator-(Point p) { return Point(add(x, -p.x), add(y, -p.y)); }
  void operator-=(Point p) {
    x = add(x, -p.x);
    y = add(y, -p.y);
  }
  Point operator*(double a) { return Point(x * a, y * a); }
  double operator*(Point p) { return dot(p); }
  Point operator/(double a) { return Point(x / a, y / a); }

  double norm() { return sqrt(x * x + y * y); }
  double dot(Point p) { return add(x * p.x, y * p.y); }
  double rot(Point p) { return add(x * p.y, -y * p.x); }
  double add(double a, double b) {
    double EPS = 1e-10;
    if (abs(a + b) < EPS * (abs(a) + abs(b))) {
      return 0;
    }
    return a + b;
  }
};
istream &operator>>(istream &in, Point &P) {
  in >> P.x >> P.y;
  return in;
}
bool operator==(Point A, Point B) {
  if (A.x == B.x && A.y == B.y)
    return true;
  return false;
}
bool operator<(Point A, Point B) {
  if (A.x < B.x)
    return true;
  else if (A.x > B.x)
    return false;
  if (A.y < B.y)
    return true;
  return false;
}
bool operator>(Point A, Point B) {
  if (A < B)
    return false;
  if (A == B)
    return false;
  return true;
}

// 線分で表した直線の交差判定
bool is_cross(Point p1, Point p2, Point q1, Point q2) {
  double res = (p2 - p1).rot(q2 - q1);
  return res != 0; // 平行なら0
}

/*ccwへ//線分p1-p2上に点qがあるか判定
bool on_seg(Point p1,Point p2,Point q){
        return (p1-q).rot(p2-q) == 0 && (p1-q).dot(p2-q) <= 0;
}*/
// 直線p1-p2と直線q1-q2の交点
// 交差判定をしてから使う:0除算
Point intersection(Point p1, Point p2, Point q1, Point q2) {
  return p1 + (p2 - p1) * ((q2 - q1).rot(q1 - p1) / (q2 - q1).rot(p2 - p1));
}

// 線分ABに対する点C
enum PointPotion {
  ONLINE_BACK = -2,
  CLOCKWISE,
  ON_SEGMENT,
  COUNTER_CLOCKWISE,
  ONLINE_FRONT
};
PointPotion ccw(Point A, Point B, Point C) {
  B -= A;
  C -= A;
  if (B.rot(C) > 0)
    return COUNTER_CLOCKWISE; //+1
  if (B.rot(C) < 0)
    return CLOCKWISE; //-1
  if (B.dot(C) < 0)
    return ONLINE_BACK; //-2
  if (B.norm() < C.norm())
    return ONLINE_FRONT; //+2
  return ON_SEGMENT;     // 0
}
// 線分p1-p2,と線分q1-q2の交差判定
// http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_2_B
bool intersect(Point p1, Point p2, Point q1, Point q2) {
  return (ccw(p1, p2, q1) * ccw(p1, p2, q2) <= 0) &&
         (ccw(q1, q2, p1) * ccw(q1, q2, p2) <= 0);
}
///
// 直線p1-p2と点q1の距離
double dist_LineP(Point p1, Point p2, Point q1) {
  return abs((p2 - p1).rot(q1 - p1)) / (p2 - p1).norm();
}
// 線分p1-p2と点q1の距離
double dist_SegP(Point p1, Point p2, Point q1) {
  //(日)
  if ((p2 - p1).dot(q1 - p1) < 0) {
    return (q1 - p1).norm(); // p1から見てp2と逆方向
  }
  if ((p1 - p2).dot(q1 - p2) < 0) {
    return (q1 - p2).norm(); // p2から見てp1と逆方向
  }
  return dist_LineP(p1, p2, q1); // 垂線下ろす
}
// 線分同士の最短距離
// http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_2_D
// http://judge.u-aizu.ac.jp/onlinejudge/review.jsp?rid=862507#1
double dist_segseg(Point A1, Point A2, Point B1, Point B2) {
  if (intersect(A1, A2, B1, B2)) {
    return 0;
  }
  return min(min(dist_SegP(A1, A2, B1), dist_SegP(A1, A2, B2)),
             min(dist_SegP(B1, B2, A1), dist_SegP(B1, B2, A2)));
}
#pragma endregion // class Point
#pragma region CGL
// 多角形内なら2,線上なら1,外なら0
// http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=CGL_3_C
// http://www.prefield.com/algorithm/geometry/contains.html
// 点Pから半直線を引く、ガウス
int contains(vector<Point> &v, Point &P) {
  bool in = false;
  const int N = v.size();
  for (int i = 0; i < N; ++i) {
    Point A = (v[i] - P);
    Point B = (v[(i + 1) % N] - P);
    if (A.y > B.y)
      swap(A, B);
    if (A.y <= 0 && 0 < B.y) {
      if (A.rot(B) < 0)
        in = !in;
    }
    if (A.rot(B) == 0 && A.dot(B) <= 0) {
      return 1; // ON 線上
    }
  }
  return in ? 2 : 0; // 中:外
}
#pragma endregion // contains
#pragma region CGL
// 辞書順で比較
bool cmp_x(const Point &p, const Point &q) {
  if (p.x != q.x)
    return p.x < q.x;
  return p.y < q.y;
}

// 凸包を求める
vector<Point> convex_hull(vector<Point> ps, int n) {
  sort(ps.begin(), ps.end(), cmp_x);
  int k = 0;               // 凸包の頂点数
  vector<Point> qs(n * 2); // 構築中の凸包
  // 下側の凸包の作成
  for (int i = 0; i < n; ++i) {
    while (k > 1 && (qs[k - 1] - qs[k - 2]).rot(ps[i] - qs[k - 1]) <=
                        0) { //<で線上も加える
      k--;
    }
    qs[k++] = ps[i];
  }
  // 上側凸包の作成
  for (int i = n - 2, t = k; i >= 0; i--) {
    while (k > t && (qs[k - 1] - qs[k - 2]).rot(ps[i] - qs[k - 1]) <= 0) { //<
      k--;
    }
    qs[k++] = ps[i];
  }
  qs.resize(k - 1);
  return qs;
}
#pragma endregion // 凸包
#pragma region CGL
double area(vector<Point> poly) {
  int size = poly.size();
  double ans = 0;
  for (int i = 1; i < size - 1; ++i) {
    ans += (poly[i] - poly[0]).rot(poly[i + 1] - poly[0]) / 2;
  }
  return ans;
}
#pragma endregion // 多角形の面積
#pragma region CGL
bool compare_x(Point A, Point B) { return A.x < B.x; }
bool compare_y(Point A, Point B) { return A.y < B.y; }
// vecはx座標の昇順で渡される
double closest_pair(vector<Point>::iterator itr, int N) {
  if (N <= 1)
    return INF;
  int m = N / 2;
  double x = (itr + m)->x;
  double d = min(closest_pair(itr, m), closest_pair((itr + m), N - m));

  inplace_merge(itr, itr + m, itr + N, compare_y);

  vector<Point> B;
  for (int i = 0; i < N; ++i) {
    if (fabs((itr + i)->x - x) >= d)
      continue;
    int Bsize = B.size();
    for (int j = 0; j < Bsize; j++) {
      double dx, dy;
      dx = (itr + i)->x - B[Bsize - j - 1].x;
      dy = (itr + i)->y - B[Bsize - j - 1].y;
      if (dy >= d)
        break;
      d = min(d, hypot(dx, dy));
    }
    B.push_back(*(itr + i));
  }
  return d;
}
#pragma endregion // 最近対 2D
#pragma region CGL
int CircleIntersection(Point A, double AR, Point B, double BR) {
  double D = (B - A).norm();
  if (D > AR + BR) {
    return 4;
  } else if (D == AR + BR) {
    return 3;
  } else if (abs(AR - BR) < D) { //&& D<AR+BR
    return 2;
  } else if (D == abs(AR - BR)) {
    return 1;
  } else if (D + AR < BR || D + BR < AR) {
    return 0;
  }
  return 0; //
}
#pragma endregion // 円と円の位置関係
#pragma region CGL
vector<Point> CircleLine(Point C, double CR, Point A, Point B) {
  vector<Point> ans(2); // 同じ交点なら同じ値
  double a, b, c;
  a = -(A.y - B.y);
  b = A.x - B.x;
  c = -(a * A.x + b * A.y);

  double l, k, d;
  l = a * a + b * b;
  k = a * C.x + b * C.y + c;
  d = l * CR * CR - k * k;
  if (d > 0) {
    double ds = sqrt(d);
    double apl = a / l;
    double bpl = b / l;
    double xc = C.x - apl * k;
    double yc = C.y - bpl * k;
    double xd = bpl * ds;
    double yd = apl * ds;
    Point temp;
    ans[0].x = xc - xd;
    ans[0].y = yc + yd;
    ans[1].x = xc + xd;
    ans[1].y = yc - yd;
  } else if (d == 0) {
    Point temp;
    temp.x = C.x - a * k / l;
    temp.y = C.y - b * k / l;
    ans[0] = temp;
    ans[1] = temp;
  } else {
    Point temp;
    temp.x = INF;
    temp.y = INF;
    ans[0] = temp;
    ans[1] = temp;
  }
  return ans;
}
#pragma endregion // 円と直線の交点,距離チェックする。

#pragma region DSL
class UnionFind {
public:
  int cNum; // 要素数
  vector<int> parent;
  vector<int> count;
  vector<vector<int>> GList;
  UnionFind(int n) {
    cNum = n;
    parent = vector<int>(n);
    count = vector<int>(n, 1);
    GList.resize(n);
    for (int i = 0; i < n; ++i) {
      parent[i] = i;
      GList[i].push_back(i);
    }
  }
  int find(int x) {
    if (parent[x] == x) {
      return x;
    }
    return parent[x] = find(parent[x]);
  }
  bool same(int x, int y) { return find(x) == find(y); }
  int Count(int x) { return count[find(x)]; }
  void add(int x, int y) { // union
    x = find(x);
    y = find(y);
    if (x == y)
      return;
    parent[x] = y;

    count[y] += count[x];
    if (GList[y].size() < GList[x].size()) {
      swap(GList[x], GList[y]);
    }
    GList[y].insert(GList[y].end(), GList[x].begin(), GList[x].end());
  }
};

#pragma endregion // UnionFind
#pragma region DSL
class segment {};
#pragma endregion // segment tree
#pragma region DSL
class BITree { // 1-index
  int N;
  vector<LL> bit;

public:
  BITree(int n) {
    N = n;
    bit = vector<LL>(N + 1, 0); // 1-index
  }
  void add(int a, LL w) { // aにwを足す
    if (a <= 0 || N < a)
      return; // a:[1,N]
    for (int i = a; i <= N; i += i & -i) {
      bit[i] += w;
    }
  }
  LL sum(int a) { //[1,a]の和,a:[1,N]
    /*
    1番目からa番目までの和、1-index
    */
    LL ret = 0;
    if (a > N)
      a = N;
    for (int i = a; i > 0; i -= i & -i) {
      ret += bit[i];
    }
    return ret;
  }
};
#pragma endregion // BIndexTree

#pragma region
template <class T, class U> istream &operator>>(istream &in, pair<T, U> &P) {
  in >> P.first >> P.second;
  return in;
}
#pragma endregion // cin pair<T,U>
#pragma region
template <class T> istream &operator>>(istream &in, vector<T> &v) {
  int size = v.size();
  for (int i = 0; i < size; ++i) {
    in >> v[i];
  }
  return in;
}
#pragma endregion // cin vector<int>
#pragma region
// 行列の積
namespace mymat {
LL matMOD = MOD; // 初期値10^9 + 7
};
template <class T>
vector<vector<T>> operator*(vector<vector<T>> &A, vector<vector<T>> &B) {
  LL mod = mymat::matMOD;
  int R = A.size();
  int cen = A[0].size();
  int C = B[0].size();
  vector<vector<T>> ans(R, vector<T>(C, 0));
  for (int row = 0; row < R; ++row) {
    for (int col = 0; col < C; ++col) {
      for (int inner = 0; inner < cen; ++inner) {
        ans[row][col] = (ans[row][col] + A[row][inner] * B[inner][col]) % mod;
        // ans[row][col] = (ans[row][col] + A[row][inner]*B[inner][col]);
      }
    }
  }
  return ans;
}

template <class T>
vector<vector<T>> powMod(vector<vector<T>> mat, LL N, LL mod = MOD) {
  mymat::matMOD = mod;
  int R = mat.size();
  int C = mat[0].size();
  // R==C
  vector<vector<T>> I(R, vector<T>(C, 0)); // 単位元
  for (int i = 0; i < R && i < C; ++i) {
    I[i][i] = 1;
  }
  if (N == 0) {
    return I;
  }
  vector<vector<T>> mul(R, vector<T>(C)), ans(R, vector<T>(C));
  ans = I;
  mul = mat;
  while (N) {
    if (N & 1) {
      ans = ans * mul;
    }
    N >>= 1;
    mul = mul * mul;
  }
  return ans;
}
#pragma endregion // 行列

#pragma region
namespace TIME {
time_t start, limit;
void time_start() { start = time(NULL); }
void time_set(int num) { limit = num; } // 秒
bool check() { return (time(NULL) - start < limit); }
} // namespace TIME
#pragma endregion // 時間計測

#pragma region
/*
namespace RAND{
mt19937 mt;
void rand_init(){
        random_device rnd;
        mt = mt19937(rnd());
}
int rand(){
        return mt();
}
}
*/
#pragma endregion // 乱数

#pragma region
#pragma endregion //

//////////////////
template <typename T> class segment_base {
  int N; // 要素数
  vector<T> dat1;
  T VAL_E; // 初期値
public:
  segment_base(){};
  segment_base(int n, T val_E) : N(n), VAL_E(val_E) {
    dat1.resize(2 * n);
    dat1.assign(2 * n, val_E); // 初期化
  }
  void init(int n, T val_E) {
    N = n;
    VAL_E = val_E;
    dat1.resize(2 * n);
    dat1.assign(2 * n, val_E);
  }
  T SELECT(T L, T R) { // 扱う演算子
    T ans;
    ans = min(L, R); //
    return ans;
  }

  // index番目の値をvalに変更,indexは"0-index"
  void update(int index, T val) {
    for (dat1[index += N] = val; index > 1; index >>= 1) {
      dat1[index >> 1] = SELECT(dat1[index], dat1[index ^ 1]); // index+0,+1
    }
  }

  // 区間[L,R)のSELECT
  T query(int L, int R) {
    T ans = VAL_E; //
    for (L += N, R += N; L < R; L >>= 1, R >>= 1) {
      if (L & 1)
        ans = SELECT(ans, dat1[L++]);
      if (R & 1)
        ans = SELECT(ans, dat1[--R]);
    }
    return ans;
  }
};
//////////////////
vector<int> A;
vector<int> Aindex;       // Aの値からインデックスをえる。
segment_base<int> seg[2]; // 偶数、奇数0-index

void solve() {
  int N;
  cin >> N;
  A.resize(N);
  Aindex.resize(N + 1);
  seg[0].init(N, INF);
  seg[1].init(N, INF);

  for (int i = 0; i < N; ++i) {
    cin >> A[i];
    Aindex[A[i]] = i;
    seg[i & 1].update(i, A[i]);
  }

  vector<int> start(3);
  start[1] = 0;
  start[2] = N;
  start[0] = seg[start[1] & 1].query(start[1], start[2]);
  priority_queue<vector<int>, vector<vector<int>>, greater<vector<int>>> que;
  que.push(start);
  int pos = 0;
  vector<int> ans(N);
  vector<int> temp(3);
  while (!que.empty()) {
    temp = que.top();
    que.pop();
    int Lval, Rval; // 値
    Lval = temp[0];
    int Lindex = Aindex[Lval];

    Rval = seg[(Lindex & 1) ^ 1].query(Lindex, temp[2]); //
    int Rindex = Aindex[Rval];

    ans[pos++] = Lval;
    ans[pos++] = Rval;

    // 区間の分割	,取った間は偶奇がずれる。
    vector<int> next(3);
    if (temp[1] < Lindex) {
      next[1] = temp[1];
      next[2] = Lindex;
      next[0] = seg[next[1] & 1].query(next[1], next[2]);
      que.push(next);
    }
    if (Lindex + 1 < Rindex) {
      next[1] = Lindex + 1;
      next[2] = Rindex;
      next[0] = seg[next[1] & 1].query(next[1], next[2]);
      que.push(next);
    }
    if (Rindex + 1 < temp[2]) {
      next[1] = Rindex + 1;
      next[2] = temp[2];
      next[0] = seg[next[1] & 1].query(next[1], next[2]);
      que.push(next);
    }
  }

  for (int i = 0; i < N; ++i) {
    if (i)
      cout << " ";
    cout << ans[i];
  }
  cout << endl;
}

#pragma region main
signed main(void) {
  std::cin.tie(0);
  std::ios::sync_with_stdio(false);
  std::cout << std::fixed; // 小数を10進数表示
  cout << setprecision(16); // 小数点以下の桁数を指定//coutとcerrで別

  solve();
}
#pragma endregion // main()