#include<bits/stdc++.h>
//ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
//clock_t start=clock();clock_t end=clock();cout<<(double)(end-start)/CLOCKS_PER_SEC<<endl;
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef unsigned int ui;
typedef pair<int,int> pii;
typedef pair<pii,int> ppii;
typedef pair<int,pii> pipi;
typedef pair<ll,ll> pll;
typedef pair<pll,ll> ppll;
typedef pair<ll,pll> plpl;
typedef tuple<ll,ll,ll> tl;
typedef pair<double,double> pdd;
typedef vector<vector<ll>> mat;
ll mod=1000000007;
ll mod2=998244353;
ll mod3=1000003;
ll mod4=998244853;
ll mod5=1000000009;
ll inf=1LL<<60;
double pi=3.141592653589793238462643383279L;
double eps=1e-14;
#define rep(i,m,n) for(ll i=m;i<n;i++)
#define rrep(i,n,m) for(ll i=n;i>=m;i--)
#define srep(itr,st) for(auto itr=st.begin();itr!=st.end();itr++)
#define mrep(itr,mp) for(auto itr=mp.begin();itr!=mp.end();itr++)
#define Max(a,b) a=max(a,b)
#define Min(a,b) a=min(a,b)
int dh[4]={1,-1,0,0};
int dw[4]={0,0,1,-1};
int ddh[8]={-1,-1,-1,0,0,1,1,1};
int ddw[8]={-1,0,1,-1,1,-1,0,1};
ll gcd(ll a,ll b){
    if(a<b)swap(a,b);
    if(b==0)return a;
    if(a%b==0)return b;
    return gcd(b,a%b);
}
ll Pow(ll n,ll k){
    ll ret=1;
    ll now=n;
    while(k>0){
        if(k&1)ret*=now;
        now*=now;
        k/=2;
    }
    return ret;
}
ll beki(ll n,ll k,ll md){
  ll ret=1;
  ll now=n;
  while(k>0){
    if(k%2==1){
      ret*=now;
      ret%=md;
    }
    now*=now;
    now%=md;
    k/=2;
  }
  return ret;
}
ll gyaku(ll n,ll md){
  return beki(n,md-2,md);
}
ll popcount(ll n){
    ll ret=0;
    ll u=n;
    while(u>0){
        ret+=u%2;
        u/=2;
        
    }
    return ret;
}
int p[200010];
struct ST{
private:
    ll n;
    vector<pll> dat;
public:
    ST(vector<ll> v){
        ll sz=v.size();
        n=1;while(n<sz)n*=2;
        pll p={inf,inf};
        dat.resize(2*n-1,p);
        rep(i,0,sz)dat[i+n-1]={v[i],i};
        rrep(i,n-2,0){
            dat[i]=min(dat[i*2+1],dat[i*2+2]);
        }
    }
    void add(ll k,ll x){
        ll i=k+n-1;
        dat[i]={x,k};
        while(i>0){
            i=(i-1)/2;
            dat[i]=min(dat[2*i+1],dat[2*i+2]);
        }
    }
    pll que(ll a,ll b,ll k=0,ll l=0,ll r=-1){
        if(r<0)r=n;
        if(b<=l||a>=r)return {inf,inf};
        if(a<=l&&b>=r)return dat[k];
        pll m1=que(a,b,2*k+1,l,(l+r)/2);
        pll m2=que(a,b,2*k+2,(l+r)/2,r);
        return min(m1,m2);
    }
};
typedef pair<pll,pll> pllp;
typedef pair<pll,pllp> pp;
ST seg1(vector<ll>(200010,inf)),seg2(vector<ll>(200010,inf));
vector<ll> ans;
priority_queue<pp,vector<pp>,greater<pp>> q;
void dfs(ll l,ll r,ll s){
    if(r-l<=1)return;
    pll p;
    if(s==0)p=seg1.que(l,r);
    else p=seg2.que(l,r);
    ll num=p.second;
    pll ppp;
    if(s==0)ppp=seg2.que(num+1,r);
    else ppp=seg1.que(num+1,r);
    ll num2=ppp.second;
    q.push({{p.first,ppp.first},{{l,r},{num,num2}}});
}
int main(){
    ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    int n;cin>>n;
    rep(i,0,n){
        cin>>p[i];
        if(i%2==0)
            seg1.add(i,p[i]);
         else   seg2.add(i,p[i]);
        
    }
    dfs(0,n,0);
    while(q.size()>0){
        pp p=q.top();q.pop();
        pll a=p.first,b=p.second.first,c=p.second.second;
        cout<<a.first<<" "<<a.second<<" ";
        dfs(b.first,c.first,(b.first)%2);
        dfs(c.first+1,c.second,(c.first+1)%2);
        dfs(c.second+1,b.second,(c.second+1)%2);
    }
  cout<<endl;
}


Measured memory_bytes: 22500