#include "bits/stdc++.h"
using namespace std;

#define REP(i, n) for(ll i = 0;i < n;i++)
#define REPR(i, n) for(ll i = n;i >= 0;i--)
#define FOR(i, m, n) for(ll i = m;i < n;i++)
#define FORR(i, m, n) for(ll i = m;i >= n;i--)
#define REPO(i, n) for(ll i = 1;i <= n;i++)
#define ll long long
#define INF (ll)1ll << 60
#define MINF (-1 * INF)
#define ALL(n) n.begin(),n.end()
#define MOD (ll)1000000007
#define P pair<ll, ll>

int n, nxt[210000], prv[210000], s[210000];
vector<int> ans;

int main(){
    cin >> n;
    REP(i, n)cin >> s[i];
    REP(i, n){
        prv[s[i]] = (i == 0 ? -1 : s[i - 1]);
        nxt[s[i]] = (i == n - 1 ? -1 : s[i + 1]);
    }
    REPO(i, n){
        if(nxt[i] != -1){
            ans.push_back(i);
            ans.push_back(nxt[i]);
            if(prv[i] != -1) nxt[prv[i]] = nxt[nxt[i]];
            if(nxt[nxt[i]] != -1) prv[nxt[nxt[i]]] = prv[i];
            nxt[i] = nxt[nxt[i]] = -1;
        }
    }
    REP(i, n) {
        cout << ans[i] << " ";
    }
    cout << endl;
}