#include <bits/stdc++.h>
using namespace std;
bool compare(int a,int b){
	return a > b;
}

int main(){
	int r[4010],i,n,k = 0,x;
	cin>>n;
	for(i = 0;i < n;i++){
		cin>>x;
		while(x != 0){
			r[k] = x % 10;
			x = x / 10;
			k++;
		}
	}	
	
	sort(r,r+k,compare);
	for(i = 0;i < k;i++){
		cout<<r[i];
	}
	
}

/**************************************************************
	Problem: 1458
	User: admin
	Language: C++
	Result: Accepted
	Time:20 ms
	Memory:2076 kb
****************************************************************/