#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: wangyiyang
	Language: C++
	Result: Accepted
	Time:17 ms
	Memory:2076 kb
****************************************************************/