#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <numeric>
#include <string>
#include <algorithm>
#include <iostream>
#include <vector>
#include <bitset>
#include <queue>
#include <map>
#include <utility>
#include <functional>
#include <unordered_map>
#include <set>
using namespace std;
typedef unsigned long long ull;
typedef long long ll;
#define MOD 1000000007           //10億　= 10^9になってる
#define juu 100000               //10万 10e5
#define hyaku 1000000            //100万　10e6
#define mINF -922337200085470000 //llのmax-1桁の小さい方
#define pINF 922337203600070000  //llのmax-1桁のデカい方
#define uINF 1844674407300000000 //ullのmax-1桁してる
#define pi 3.1415926535897932384
#define all(v) v.begin(), v.end()
#define rep(i, n) for (ll i = 0; i < (int)(n); i++)
ll factor[300];
ll memory[300];
/*素朴法で計算
factorは必ずmemset(factor,0,sizeof(factor));
グローバルであるmemoryに個数を書き込む
memory配列の走査にはfactorの要素を使う*/
void primefac(ll num)
{
    int i = 0, kosuu = 0;
    while (*(factor + i) != 0)
    {
        while (num % *(factor + i) == 0)
        {
            num /= *(factor + i);
            memory[*(factor + i)] += 1;
        }
        if (num == 1)
            break;
        i++;
    }
}
/*グローバルにあるfactorに素数書き込む.個数を返すので配列は-1しろforは<*/
int elast(ll number)
{
    ll tmp = 0;
    int flag = 0;
    *factor = 2;
    for (int i = 3; i <= number; i++)
    {
        flag = 0;
        for (int j = 0; j <= tmp; j++)
        {
            if (i % (*(factor + j)) == 0)
            {
                flag = 1;
                break;
            }
        }
        if (flag)
            continue;
        tmp += 1;
        *(factor + tmp) = i;
    }
    return tmp + 2;
}

/*intで収まる範囲であってくれ*/
ll nCr(ll n, ll r)
{
    ll val = 1;
    ll i;
    if (r == 0)
        return 1;
    for (i = 0; i < n - r; i++)
    {
        val *= (n - i);
        val /= (i + 1);
    }
    return val;
}
/*intで収まる範囲であってくれ*/
ll nPr(ll n, ll r)
{
    ll val = 1;
    ll i;
    for (i = 0; i < r; i++)
    {
        val *= (n - i);
    }
    return val;
}
template <typename T>
bool chmin(T &a, const T b)
{
    if (a > b)
    {
        a = b;
        return true;
    }
    return false;
}
template <typename T>
bool chmax(T &a, const T b)
{
    if (a < b)
    {
        a = b;
        return true;
    }
    return false;
}

/*ソートして被りを無くす*/
template <typename T>
void eraseSame(T &a)
{
    sort(all(a));
    a.erase(unique(all(a)), a.end());
}

/*aとbで大きい方を後ろにする。変更なしならtrue、ありならfalse */
template <typename T>
bool swapmax(T &a, T &b)
{
    T temp;
    temp = a;
    if (a > b)
    {
        a = b;
        b = temp;
        return false;
    }
    return true;
}
ll gcd(ll x, ll y) { return (x % y) ? gcd(y, x % y) : y; }
ll lcm(ll x, ll y) { return x / gcd(x, y) * y; }

/*一行に入力が何個あるかを1,ぶち込むvectorを2*/
template <typename T>
void splitIn(ll N, vector<T> &array)
{
    T temp;
    int i = 0;
    if (N == 0)
    {
        return;
    }
    array.resize(N);
    while (cin >> temp)
    {
        array[i] = temp;
        sort(all(array[i]));
        i++;
        if (i >= N)
        {
            break;
        }
    }
    return;
}
int main()
{
    ll n;
    cin >> n;
    vector<string> v;
    splitIn(n, v);
    string fi = v[0];
    string ans;
    sort(all(fi));
    for(auto &d:v){
        rep(i,fi.size()){
            ans = "";
            if(d.find(fi[i]) == string::npos){
                fi.erase(i,1);
                i--;
            }
            else{
                ans+=fi[i];
                d.erase(d.find(fi[i]),1);
            }
        }
        //cout << "fi:" +fi<<endl;
    }
    sort(all(fi));
    cout << fi;
    return 0;
}


/*
3
werwerwer
werwerwet
qwe


*/

Measured memory_bytes: 256