import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.InputMismatchException;
 
public class Main {
	InputStream is;
 
	int __t__ = 1;
	int __f__ = 0;
	int __FILE_DEBUG_FLAG__ = __f__;
	String __DEBUG_FILE_NAME__ = "src/B3";
 
	FastScanner in;
	PrintWriter out;
	
	boolean ok(String a, String b) {
		if (a.length() > b.length()) return true;
		if (a.length() < b.length()) return false;
		return a.compareTo(b) < 0;
	}
	
	public void solve() {
		int n = in.nextInt();
		String[] s = in.nextStringArray(n);
		
		int[][] cnt = new int[n][26];
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < s[i].length(); j++) {
				cnt[i][s[i].charAt(j)-'a']++;
			}
		}
		
		String res = "";
		for (int j = 0; j < 26; j++) {
			int min = Integer.MAX_VALUE;
			for (int i = 0; i < n; i++) {
				min = Math.min(min, cnt[i][j]);
			}
			for (int i = 0; i < min; i++) {
				res += (char)('a' + j);
			}
		}
		System.out.println(res);
	}
	
	public void run() {
		if (__FILE_DEBUG_FLAG__ == __t__) {
			try {
				is = new FileInputStream(__DEBUG_FILE_NAME__);
			} catch (FileNotFoundException e) {
				// TODO 自動生成された catch ブロック
				e.printStackTrace();
			}
			System.out.println("FILE_INPUT!");
		} else {
			is = System.in;
		}
		in = new FastScanner(is);
		out = new PrintWriter(System.out);
 
		solve();
	}
 
	public static void main(String[] args) {
		new Main().run();
	}
 
	public void mapDebug(int[][] a) {
		System.out.println("--------map display---------");
 
		for (int i = 0; i < a.length; i++) {
			for (int j = 0; j < a[i].length; j++) {
				System.out.printf("%3d ", a[i][j]);
			}
			System.out.println();
		}
 
		System.out.println("----------------------------");
		System.out.println();
	}
 
	public void debug(Object... obj) {
		System.out.println(Arrays.deepToString(obj));
	}
 
	class FastScanner {
		private InputStream stream;
		private byte[] buf = new byte[1024];
		private int curChar;
		private int numChars;
 
		public FastScanner(InputStream stream) {
			this.stream = stream;
			//stream = new FileInputStream(new File("dec.in"));
 
		}
 
		int read() {
			if (numChars == -1)
				throw new InputMismatchException();
			if (curChar >= numChars) {
				curChar = 0;
				try {
					numChars = stream.read(buf);
				} catch (IOException e) {
					throw new InputMismatchException();
				}
				if (numChars <= 0)
					return -1;
			}
			return buf[curChar++];
		}
 
		boolean isSpaceChar(int c) {
			return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
		}
 
		boolean isEndline(int c) {
			return c == '\n' || c == '\r' || c == -1;
		}
 
		int nextInt() {
			return Integer.parseInt(next());
		}
 
		int[] nextIntArray(int n) {
			int[] array = new int[n];
			for (int i = 0; i < n; i++)
				array[i] = nextInt();
 
			return array;
		}
 
		int[][] nextIntMap(int n, int m) {
			int[][] map = new int[n][m];
			for (int i = 0; i < n; i++) {
				map[i] = in.nextIntArray(m);
			}
			return map;
		}
 
		long nextLong() {
			return Long.parseLong(next());
		}
 
		long[] nextLongArray(int n) {
			long[] array = new long[n];
			for (int i = 0; i < n; i++)
				array[i] = nextLong();
 
			return array;
		}
 
		long[][] nextLongMap(int n, int m) {
			long[][] map = new long[n][m];
			for (int i = 0; i < n; i++) {
				map[i] = in.nextLongArray(m);
			}
			return map;
		}
 
		double nextDouble() {
			return Double.parseDouble(next());
		}
 
		double[] nextDoubleArray(int n) {
			double[] array = new double[n];
			for (int i = 0; i < n; i++)
				array[i] = nextDouble();
 
			return array;
		}
 
		double[][] nextDoubleMap(int n, int m) {
			double[][] map = new double[n][m];
			for (int i = 0; i < n; i++) {
				map[i] = in.nextDoubleArray(m);
			}
			return map;
		}
 
		String next() {
			int c = read();
			while (isSpaceChar(c))
				c = read();
			StringBuilder res = new StringBuilder();
			do {
				res.appendCodePoint(c);
				c = read();
			} while (!isSpaceChar(c));
			return res.toString();
		}
 
		String[] nextStringArray(int n) {
			String[] array = new String[n];
			for (int i = 0; i < n; i++)
				array[i] = next();
 
			return array;
		}
 
		String nextLine() {
			int c = read();
			while (isEndline(c))
				c = read();
			StringBuilder res = new StringBuilder();
			do {
				res.appendCodePoint(c);
				c = read();
			} while (!isEndline(c));
			return res.toString();
		}
	}
}
 

Measured memory_bytes: 21588