#include <bits/stdc++.h>

using namespace std;
#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int const maxn = 4e6 + 7;
long long const mod = 1000000007;
map<char, int> suff[maxn];
int link[maxn], len[maxn], k, from[maxn];
int sz = 2, last = 1;
string word;
char a[200007];

bitset<10> cnt[maxn];

char sym[maxn];


bool used[maxn];

void input() {
    cin >> k;
}


inline void extend(char c) {
    int curr = sz++;
    sym[curr] = c;
    from[curr] = last;
    len[curr] = len[last] + 1;
    int p;
    for (p = last; p != 0 && !suff[p][c]; p = link[p]) {
        suff[p][c] = curr;
    }
    if (p == 0) {
        link[curr] = 1;
    } else {
        int q = suff[p][c];
        if (len[p] + 1 == len[q]) {
            link[curr] = q;
        } else {
            int clone = sz++;
            from[clone] = p;
            sym[clone] = sym[q];
            len[clone] = len[p] + 1;
            link[clone] = link[q];
            suff[clone] = suff[q];
            for (; p != 0 && suff[p][c] == q; p = link[p]) {
                suff[p][c] = clone;
            }
            link[q] = link[curr] = clone;
        }
    }
    last = curr;
}

void deep_dfs(int v) {
    if ((int) sym[v] < 97) {
        cnt[v][(int) sym[v] - 60] = true;
        return;
    }
    used[v] = true;
    for (auto it:suff[v]) {
        if (!used[it.second]) {
            deep_dfs(it.second);
        }
        cnt[v] |= cnt[it.second];
    }
}


void solve() {
    sym[1] = 'a';
    for (int i = 0; i < k; i++) {
        cin >> word;
        for (size_t j = 0; j < word.length(); j++) {
            extend(word[j]);
        }
        extend((char) (60 + i));
    }
    fill(used, used + maxn, false);
    deep_dfs(1);
    int ans = 0, ind = 1;
    for (int i = 2; i < sz; i++) {
        if (cnt[i].count() == k) {
            if (len[i] > ans) {
                ans = len[i];
                ind = i;
            }
        }
    }
    int pos = 0;
    for (; ind != 1; ind = from[ind]) {
        a[pos] = sym[ind];
        pos++;
    }
    for (int i = pos - 1; i >= 0; i--) {
        cout << a[i];
    }

}

int32_t main() {
    IOS
    input();
    solve();
    return 0;

}