//yukicoder@cpp17

#include <iostream>
#include <iomanip>

#include <algorithm>

#include <cmath>
#include <cctype>
#include <climits>
#include <cassert>

#include <string>
#include <vector>
#include <set>
#include <stack>
#include <queue>
#include <map>

#include <random>

#include <bitset>

#include <complex>

#include <utility>

#include <numeric>

#include <functional>


using namespace std;
using ll = long long;
using P = pair<ll,ll>;


const ll MOD = 998244353;
const ll MODx = 1000000007;
const int INF = (1<<30)-1;
const ll LINF = (1LL<<62LL)-1;
const double EPS = (1e-10);


P ar4[4] = {{0,1},{0,-1},{1,0},{-1,0}};
P ar8[8] = {{-1,-1},{-1,0},{-1,1},{0,-1},{0,1},{1,-1},{1,0},{1,1}};


template <typename T> vector<T> make_vector(size_t a, T b) { return vector<T>(a, b); }
template <typename... Ts> auto make_vector(size_t a, Ts... ts) { return vector<decltype(make_vector(ts...))>(a, make_vector(ts...)); }
 
/*
確認ポイント
cout << fixed << setprecision(n) << 小数計算//n桁の小数表記になる

計算量は変わらないが楽できるシリーズ
min(max)_element(iter,iter)で一番小さい(大きい)値のポインタが帰ってくる
count(iter,iter,int)でintがiterからiterの間にいくつあったかを取得できる
*/

/* comment outed because can cause bugs
__attribute__((constructor))
void initial() {
  cin.tie(0);
  ios::sync_with_stdio(false);
}
*/
bool comp(pair<int,int> A, pair<int,int> B){
  return A.first < B.first;
}

int main(){
  int n;cin>>n;
  vector<int> A(n);
  for(int i = 0; n > i; i++){
    cin>>A[i];A[i]--;
  }
  stack<int> X;
  vector<pair<int,int>> ZZ;
  vector<bool> lck(n, false);
  lck[A[n-1]] = true;
  int nw = (lck[0] ? 1 : 0);
  for(int i = 0; n > i; i++){
    if(A[i] == nw){
      ZZ.push_back({A[i], A[i+1]});
      lck[A[i]] = true;
      lck[A[i+1]] = true;
      i++;
      while(nw != n && lck[nw])nw++;
      while(X.size() && X.top() == nw){
        ZZ.push_back({X.top(), A[i+1]});
        lck[X.top()] = true;
        lck[A[i+1]] = true;
        i++;
        X.pop();
        while(nw != n && lck[nw])nw++;

      }
    }else{
      X.push(A[i]);
      if(X.size() >= 2){
        int second = X.top();X.pop();
        int first = X.top(); X.pop();
        if(first < second){
          ZZ.push_back({first,second});
          lck[first] = true;
          lck[second] = true;
        }else{
          X.push(first);
          X.push(second);
        }
      }
    }
  }
  sort(ZZ.begin(), ZZ.end(), comp);
  for(int i = 0; ZZ.size() > i; i++){
    cout << ZZ[i].first+1 << " " << ZZ[i].second+1 << " \n"[i+1 == ZZ.size()];
  }
  return 0;
}