#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);
  int n;
  cin >> n;
  vector<int> a(n);
  rep(i, n) cin >> a[i];
  map<int, int> mp;
  rep(i, n) mp[a[i]] = i;
  set<int> st;
  rep(i, n) st.insert(i);
  vector<int> ans;
  while (!mp.empty()) {
    auto [val, idx] = *mp.begin();
    auto nxt = st.upper_bound(idx);
    if (nxt == st.end()) {
      mp.erase(val);
      continue;
    }
    ans.push_back(val);
    ans.push_back(a[*nxt]);
    mp.erase(a[*nxt]);
    st.erase(*nxt);
    mp.erase(val);
    st.erase(idx);
  }
  for (int x : ans) cout << x << ' ';
  cout << '\n';
  return 0;
}