#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint1000000007;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000000000000
	

int main(){	
	
	int N;
	cin>>N;
	
	priority_queue<string,vector<string>,greater<string>> Q;
	rep(i,N){
		string s;
		cin>>s;
		s += 'z' + 1;
		Q.push(s);
	}
	
	string ans = "";
	
	while(true){
		string s = Q.top();
		if(s.size()==1)break;
		Q.pop();
		ans += s[0];
		s.erase(s.begin());
		Q.push(s);
	}
	cout<<ans<<endl;
	
	return 0;
	
}