//include
//------------------------------------------
#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <queue>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <regex>

using namespace std;

//conversion
//------------------------------------------
inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}

//math
//-------------------------------------------
template<class T> inline T sqr(T x) {return x*x;}

//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;

//container util
//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())

//repetition
//------------------------------------------
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)

//constant
//--------------------------------------------
const double EPS = 1e-10;
const double PI  = acos(-1.0);
const LL MOD = 1000000007;

//clear memory
#define CLR(a) memset((a), 0 ,sizeof(a))

//debug
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

//myfuncs
//素数判定
template<class T> inline T isPrime(T x) {
	bool ret = true;
	if (x < 2) {
		ret = false;
	}
	for (LL i = 2; i <= sqrt(x); i++) {
		if (x%i == 0) {
			ret = false;
		}
	}
	return ret;
}

//Union FInd
struct UnionFind {
	vector<int> par; // par[i]:iの親の番号　(例) par[3] = 2 : 3の親が2

	UnionFind(int N) : par(N) { //最初は全てが根であるとして初期化
		for(int i = 0; i < N; i++) par[i] = i;
	}

	int root(int x) { // データxが属する木の根を再帰で得る：root(x) = {xの木の根}
		if (par[x] == x) return x;
		return par[x] = root(par[x]);
	}

	void unite(int x, int y) { // xとyの木を併合
		int rx = root(x); //xの根をrx
		int ry = root(y); //yの根をry
		if (rx == ry) return; //xとyの根が同じ(=同じ木にある)時はそのまま
		par[rx] = ry; //xとyの根が同じでない(=同じ木にない)時：xの根rxをyの根ryにつける
	}

	bool same(int x, int y) { // 2つのデータx, yが属する木が同じならtrueを返す
		int rx = root(x);
		int ry = root(y);
		return rx == ry;
	}
};

//main code

int main(int argc, char const* argv[])
{
	int n;
	cin >> n;

	string s[n];
	bool b[26];
	int num[26] = {};
	if (n == 1) {
		string s;
		cin >> s;
		for (int i = 0; i < s.size(); i++) {
			num[s[i]  - 'a']++;
		}
		for (int i = 0; i < 26; i++) {
			for (int j = 0; j < num[i]; j++) {
				cout << char('a' + i);
			}
		}
		cout << endl;
		return 0;
	}
	for (int i = 0; i < 26; i++) {
		b[i] = false;
	}
	for (int i = 0; i < n; i++) {
		cin >> s[i];
		int numl[26] = {};
		for (int j = 0; j < s[i].size(); j++) {
			numl[s[i][j] - 'a']++;
		}
		for (int j = 0; j < 26; j++) {
			if (num[j] == 0) {
				if (i == 0) {
					b[j] = true;
					num[j] = numl[j];
				}
			}
			else if (num[j] > 0 && b[j]) {
				num[j] = min(num[j],numl[j]);
			}
		}
	}
	for (int i = 0; i < 26; i++) {
		if (b[i]) {
			for (int j = 0; j < num[i]; j++) {
				cout << char('a' + i);
			}
		}
	}
	cout << endl;
	return 0;
}


Measured memory_bytes: 256