#include <iostream>
#include <algorithm>
using namespace std;
int n;
string s[25];
int main(){
    cin >> n;
    for (int i = 0; i < n; ++i)cin >> s[i];
    sort(s,s+n);
    for (int i = n; i >= 0; --i)cout << s[i];
    return 0;
}