#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define REP(i,n) for(ll i=0;i<ll(n);i++)
#define REPE(i,l,n) for(ll i=l;i<=ll(n);i++)
#define FORA(i,I) for(const auto& i:I)
int main(){
    bool f = true;
    ll n, index = -1;
    string t = "";
    char now = '~';
    cin >> n;
    vector<string> v(n);
    REP(i, n){
        cin >> v[i];
        v[i] += "~";//番兵
    }
    while(f){
        f = false;
        now = '~';
        index = -1;

        REP(i, n){    
            if(v[i] != "~"){
                f = true;
                if(now > v[i][0]){
                    now = v[i][0];
                    index = i;
                } else if (now == v[i][0]){
                    if(v[index] > v[i]) index = i;
                }
            }
        }
        if(index >= 0){
            t += now;
            v[index].erase(0, 1);
        }
    }
    cout << t << endl;
}