int N;
string S[60];
string T;

void solve() {
	int i,j,k,l,r,x,y; string s;
	
	cin>>N;
	FOR(i,N) cin>>S[i], S[i]+="{";
	
	while(1) {
		x=-1;
		FOR(i,N) if(S[i].size()>1) {
			if(x==-1 || S[x]>S[i]) x=i;
		}
		if(x==-1) break;
		
		T+=S[x][0];
		S[x]=S[x].substr(1);
	}
	
	cout<<T<<endl;
}