import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.NoSuchElementException;
import java.util.stream.IntStream;

public class Main {

	public static void main(String[] args) throws IOException {
		new Main().solve();
	}

	private void solve() throws IOException {
		try {
			//			solveA();
			//			solveB();
			solveC();
			// solveD();
			// solveE();
			// solveF();
		} finally {
			if (in != null) {
				in.close();
			}
			if (out != null) {
				out.flush();
				out.close();
			}
		}

	}

	private void solveA() {
		int numA = nextInt();
		int numB = nextInt();
		int numC = nextInt();

		if (numB - numA == numC - numB) {
			out.println("YES");
		} else {
			out.println("NO");
		}

		out.println("");
	}

	private void solveB() {
		String strO = next();
		String strE = next();

		StringBuilder builder = new StringBuilder();
		IntStream.range(0, strO.length() + strE.length()).reduce(0, (sum, i) -> {
			if (i % 2 == 0) {
				builder.append(strO.charAt(sum));
			} else {
				builder.append(strE.charAt(sum));
				sum++;
			}
			return sum;
		});

		//		int cnt = 0;
		//		for (int i = 0; i < strO.length() + strE.length(); i++) {
		//			if (i % 2 == 0) {
		//				builder.append(strO.charAt(cnt));
		//			} else {
		//				builder.append(strE.charAt(cnt));
		//				cnt++;
		//			}
		//		}
		out.println(builder.toString());
	}

	private void solveC() {
		int numN = nextInt();
		/**
		 * 読み込みをStreamを使ってみてる
		 */
		String[] wk = IntStream.range(0, numN).mapToObj(i -> next()).toArray(String[]::new);

		int[][] array = new int[numN][26];

		for (int i = 0; i < array.length; i++) {
			for (int j = 0; j < wk[i].length(); j++) {
				int alphaIndex = wk[i].charAt(j) - 'a';
				array[i][alphaIndex] += 1;
			}
		}

		StringBuilder builder = new StringBuilder();
		for (int i = 0; i < 26; i++) {
			int res = Integer.MAX_VALUE;
			for (int j = 0; j < array.length; j++) {
				res = Math.min(res, array[j][i]);
			}
			for (int j = 0; j < res; j++) {
				builder.append((char) (i + (int) 'a'));
			}
		}

		out.println(builder.toString());
	}

	private void solveD() {
		int numN = nextInt();

		out.println("");
	}

	private void solveE() {
		int numN = nextInt();

		out.println("");
	}

	private void solveF() {
		int numN = nextInt();

		out.println("");
	}

	private final PrintWriter out = new PrintWriter(System.out);
	private final InputStream in = System.in;
	private final byte[] buffer = new byte[1024];
	private int ptr = 0;
	private int buflen = 0;

	private boolean hasNextByte() {
		if (ptr < buflen) {
			return true;
		} else {
			ptr = 0;
			try {
				buflen = in.read(buffer);
			} catch (IOException e) {
				e.printStackTrace();
			}
			if (buflen <= 0) {
				return false;
			}
		}
		return true;
	}

	private int readByte() {
		if (hasNextByte())
			return buffer[ptr++];
		else
			return -1;
	}

	private static boolean isPrintableChar(int c) {
		return 33 <= c && c <= 126;
	}

	private void skipUnprintable() {
		while (hasNextByte() && !isPrintableChar(buffer[ptr]))
			ptr++;
	}

	public boolean hasNext() {
		skipUnprintable();
		return hasNextByte();
	}

	public int nextInt() {
		return Integer.parseInt(next());
	}

	public String next() {
		if (!hasNext())
			throw new NoSuchElementException();
		StringBuilder sb = new StringBuilder();
		int b = readByte();
		while (isPrintableChar(b)) {
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}

	public long nextLong() {
		if (!hasNext())
			throw new NoSuchElementException();
		long n = 0;
		boolean minus = false;
		int b = readByte();
		if (b == '-') {
			minus = true;
			b = readByte();
		}
		if (b < '0' || '9' < b) {
			throw new NumberFormatException();
		}
		while (true) {
			if ('0' <= b && b <= '9') {
				n *= 10;
				n += b - '0';
			} else if (b == -1 || !isPrintableChar(b)) {
				return minus ? -n : n;
			} else {
				throw new NumberFormatException();
			}
			b = readByte();
		}
	}
}

Measured memory_bytes: 27220