#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;

int N;
vector<string> S;

void solve(){
    each(s, S)s += '~';
    vi kk(N);
    string ans;
    while(true){
        string mini = "~";
        int k = -1;
        rep(i, N){
            string sub = S[i].substr(kk[i]);
            if(sub < mini){
                mini = sub;
                k = i;
            }
        }
        if(k == -1){
            break;
        } else{
            ans += mini[0];
            kk[k]++;
        }
    }
    cout << ans << endl;
}

int main(){
    while(cin >> N){
        S.resize(N);
        rep(i, N)cin >> S[i];
        solve();
    }
}