#include <bits/stdc++.h>
using namespace std;
int main() {
int t;
cin>>t;
string arr,x;
for(int i=0;i<t;i++){
cin>>x;
arr+=x;
}
for(int i=0;i<arr.size()-1;i++){
for(int j=0;j<arr.size()-i-1;j++){
if(arr[j]<arr[j+1]){
int x;
x = arr[j] - '0';
arr[j] = arr[j+1] ;
arr[j+1] = x + '0';
}
}
}
for(int i=0;i<=arr.size();i++){
cout<<arr[i];
}
cout<<"\n";
return 0;
}
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