#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#define chkmax(a, b) a = max(a, b)
#define chkmin(a, b) a = min(a, b)
#define all(v) v.begin(), v.end()
#define x first
#define y second
using namespace std;
using namespace __gnu_pbds;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int, int> pii;
typedef vector<pii> vii;
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;

const int MAX_N = 1e5 + 5;

int block[MAX_N];
int n;

vii min_shooting_buildings(vi h){
    n = h.size();
    ordered_set s;
    for (int i = n - 1; i >= 0; i--) {
        block[i] = s.order_of_key(h[i]);
        s.insert(h[i]);
    }
    vii ans;
    int alive = n;
    while (alive) {
        int max_v = 0;
        int op1 = -1, op2 = -1;
        for (int i = 0; i < n; i++) {
            if (h[i] <= max_v) continue;
            max_v = h[i];
            if (op1 == -1) op1 = i;
            else if (op2 == -1) op2 = i;
            else if (block[i] > block[op1]) {
                op2 = op1;
                op1 = i;
            } else if (block[i] > block[op2]) op2 = i;
        }
        alive--;
        alive -= op2 != -1;
        if (op2 == -1) op2 = op1;
        ans.push_back({h[op1], h[op2]});
        h[op1] = h[op2] = 0;
    }
    return ans;
}