#include<bits/stdc++.h>
using namespace std;
const int N=1e5+5;
int n,f[N],a[N],ct,p[N];
bool out[N],dl[N];
vector<pair<int, int> > min_shooting_buildings(vector<int> H){
	n=H.size();
	for(int i=1;i<=n;++i){
		a[i]=H[i-1];
		for(int j=1;j<i;++j)if(!p[j]&&a[j]<a[i]){
			p[j]=i,p[i]=j;
			break;
		}
		if(p[i])continue;
		for(int j=1;j<i;++j)if(p[j]<j&&a[j]<a[i]){
			p[p[j]]=0,p[j]=i,p[i]=j;
			break;
		}
	}
	vector<pair<int,int> >ans;
	while(ct<n){
		int mx=0;
		for(int i=1;i<=n;++i)out[i]=false;
		for(int i=1;i<=n;++i)if(!dl[i]){
			mx=max(mx,a[i]);
			if(mx==a[i])out[i]=true;
		}
		bool fg=false;
		for(int i=1;i<=n;++i)if(out[i]&&!p[i]){
			ans.push_back(make_pair(a[i],a[i]));
			dl[i]=true;
			fg=true;
			break;
		}
		if(fg){
			++ct;
			continue;
		}
		for(int i=n,ls=0;i;--i)if(out[i]){
			if(out[p[i]]){
				ans.push_back(make_pair(a[i],a[p[i]]));
				dl[i]=dl[p[i]]=true;
				ct+=2;
				break;
			}else if(p[i]>i){
				p[p[i]]=p[ls];
				p[p[ls]]=p[i];
				ans.push_back(make_pair(a[i],a[ls]));
				dl[i]=dl[ls]=true;
				ct+=2;
				break;
			}
			ls=i;
		}
	}
	return ans;
}