#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
const int MAXN = 20 + 5;
string s[MAXN];
int n;

bool cmp(string x, string y){
	for (int i = 0;i < min(x.size(), y.size());i++){
		if (x[i] > y[i]){
			return true;
		}
		else if (x[i] < y[i]){
			return false;
		}
	}
}

int main(){
    cin >> n;
    for (int i = 1;i <= n;i++){
        cin >> s[i];
    }
    sort(s + 1, s + n + 1, cmp);
    for (int i = 1;i <= n;i++){
        cout << s[i];
    }
    return 0;
}