#include <bits/stdc++.h>
using namespace std;
const int N=1e5+10;
const int INF=0x3f3f3f3f;
int a[N],s[N],ans;
bool f;
int main()
{
	for(int i=1;i<=20;i++)
	{
		cin>>a[i];
	}
	sort(a+1,a+21);
	for(int i=1;i<=20;i+=2)
	{
		cout<<a[i]<<" ";
	}
	return 0;
}

#include <iostream>
#include <stdio.h>
#include <string.h>
using namespace std;
#define LL long long
const int N = 1e5 + 10;
const int INF = 0x3f3f3f3f;
int a[N];
int main()
{
	int	n = 20;
	for(int i = 0;i < 20;i++)
		cin >> a[i];
	for(int i = 0;i < n-1;i++)
	{
		for(int j = 0;j < n-i-1;j++)
		{
			if(a[j] > a[j+1])
			{
				int t = a[j];
				a[j] = a[j + 1];
				a[j+1] = t;
			}
		}
	}
	for(int i = 0 ; i < n ; i+=2)
	cout << a[i] <<" ";
}