Problem: Fox Ciel is going to publish a paper on FOCS (Foxes Operated Computer Systems, pronounce: "Fox"). She heard a rumor: the authors list on the paper is always sorted in the lexicographical order. 

After checking some examples, she found out that sometimes it wasn't true. On some papers authors' names weren't sorted in lexicographical order in normal sense. But it was always true that after some modification of the order of letters in alphabet, the order of authors becomes lexicographical!

She wants to know, if there exists an order of letters in Latin alphabet such that the names on the paper she is submitting are following in the lexicographical order. If so, you should find out any such order.

Lexicographical order is defined in following way. When we compare s and t, first we find the leftmost position with differing characters: si ≠ ti. If there is no such position (i. e. s is a prefix of t or vice versa) the shortest string is less. Otherwise, we compare characters si and ti according to their order in alphabet.

Input

The first line contains an integer n (1 ≤ n ≤ 100): number of names.

Each of the following n lines contain one string namei (1 ≤ |namei| ≤ 100), the i-th name. Each name contains only lowercase Latin letters. All names are different.

Output

If there exists such order of letters that the given names are sorted lexicographically, output any such order as a permutation of characters 'a'–'z' (i. e. first output the first letter of the modified alphabet, then the second, and so on).

Otherwise output a single word "Impossible" (without quotes).

Examples

Input

3
rivest
shamir
adleman


Output

bcdefghijklmnopqrsatuvwxyz


Input

10
tourist
petr
wjmzbmr
yeputons
vepifanov
scottwu
oooooooooooooooo
subscriber
rowdark
tankengineer


Output

Impossible


Input

10
petr
egor
endagorion
feferivan
ilovetanyaromanova
kostka
dmitriyh
maratsnowbear
bredorjaguarturnik
cgyforever


Output

aghjlnopefikdmbcqrstuvwxyz


Input

7
car
care
careful
carefully
becarefuldontforgetsomething
otherwiseyouwillbehacked
goodluck


Output

acbdefhijklmnogpqrstuvwxyz

Solution (in JAVA):

Solution:
import java.io.OutputStreamWriter;
import java.io.BufferedWriter;
import java.util.Comparator;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.io.Writer;
import java.util.List;
import java.io.IOException;
import java.util.Arrays;
import java.util.InputMismatchException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.math.BigInteger;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 * @author Stanislav Pak
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        OutputWriter out = new OutputWriter(outputStream);
        TaskA solver = new TaskA();
        solver.solve(1, in, out);
        out.close();
    }
}

class TaskA {
    public void solve(int testNumber, InputReader in, OutputWriter out) {
        int n = in.readInt();
        String[] w = new String[n];
        for (int i = 0; i < n; ++i) {
            w[i] = in.readString();
        }
        Graph graph = new Graph(26, n * n);
        boolean ok = true;
        for (int i = 0; i < n; ++i) {
            for (int j = i + 1; j < n; ++j) {
                int p = 0;
                while (p < w[i].length() && p < w[j].length() && w[i].charAt(p) == w[j].charAt(p)) {
                    ++p;
                }
                if (p == w[j].length() && p < w[i].length()) {
                    ok = false;
                    break;
                }
                if (p == w[j].length() || p == w[i].length()) continue;
                int from = w[j].charAt(p) - 'a';
                int to = w[i].charAt(p) - 'a';
                graph.addSimpleEdge(from, to);
            }
            if (!ok) break;
        }
        if (!ok) {
            out.printLine("Impossible");
            return;
        }
        int[] used = ArrayUtils.createArray(26, 0);
        List<Integer> order = new ArrayList<>(26);
        for (int v = 0; v < 26; ++v) {
            if (used[v] == 0) {
                if (!dfs(v, graph, used, order)) {
                    ok = false;
                }
            }
        }
        if (!ok) {
            out.printLine("Impossible");
            return;
        }
        assert(order.size() == 26);
        StringBuilder ans = new StringBuilder();
        for (int i = 0; i < 26; ++i) {
            char c = toChar(order.get(i));
            ans.append(c);
        }
        out.printLine(ans);
    }

    private char toChar(int i) {
        return (char) (i + 'a');
    }

    private boolean dfs(int v, Graph graph, int[] used, List<Integer> order) {
        if (used[v] > 0) return false;
        used[v] = 1;
        for (Edge edge : graph.outbound(v)) {
            if (used[edge.getDestination()] != 2) {
                if (!dfs(edge.getDestination(), graph, used, order)) {
                    return false;
                }
            }
        }
        order.add(v);
        used[v] = 2;
        return true;
    }
}

class InputReader {

    private InputStream stream;
    private byte[] buf = new byte[1024];
    private int curChar;
    private int numChars;
    private SpaceCharFilter filter;

    public InputReader(InputStream stream) {
        this.stream = stream;
    }

    public 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++];
    }

    public int readInt() {
        int c = read();
        while (isSpaceChar(c))
            c = read();
        int sgn = 1;
        if (c == '-') {
            sgn = -1;
            c = read();
        }
        int res = 0;
        do {
            if (c < '0' || c > '9')
                throw new InputMismatchException();
            res *= 10;
            res += c - '0';
            c = read();
        } while (!isSpaceChar(c));
        return res * sgn;
    }

    public String readString() {
        int c = read();
        while (isSpaceChar(c))
            c = read();
        StringBuilder res = new StringBuilder();
        do {
            if (Character.isValidCodePoint(c))
                res.appendCodePoint(c);
            c = read();
        } while (!isSpaceChar(c));
        return res.toString();
    }

    public boolean isSpaceChar(int c) {
        if (filter != null)
            return filter.isSpaceChar(c);
        return isWhitespace(c);
    }

    public static boolean isWhitespace(int c) {
        return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
    }

    public interface SpaceCharFilter {
        public boolean isSpaceChar(int ch);
    }
}

class OutputWriter {
    private final PrintWriter writer;

    public OutputWriter(OutputStream outputStream) {
        writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
    }

    public void print(Object...objects) {
        for (int i = 0; i < objects.length; i++) {
            if (i != 0)
                writer.print(' ');
            writer.print(objects[i]);
        }
    }

    public void printLine(Object...objects) {
        print(objects);
        writer.println();
    }

    public void close() {
        writer.close();
    }

}

class Graph {
    public static final int REMOVED_BIT = 0;

    protected int vertexCount;
    protected int edgeCount;

    private int[] firstOutbound;
    private int[] firstInbound;

    private Edge[] edges;
    private int[] nextInbound;
    private int[] nextOutbound;
    private int[] from;
    private int[] to;
    private long[] weight;
    public long[] capacity;
    private int[] reverseEdge;
    private int[] flags;

    public Graph(int vertexCount, int edgeCapacity) {
        this.vertexCount = vertexCount;
        firstOutbound = new int[vertexCount];
        Arrays.fill(firstOutbound, -1);

        from = new int[edgeCapacity];
        to = new int[edgeCapacity];
        nextOutbound = new int[edgeCapacity];
        flags = new int[edgeCapacity];
    }

    public int addEdge(int fromID, int toID, long weight, long capacity, int reverseEdge) {
        ensureEdgeCapacity(edgeCount + 1);
        if (firstOutbound[fromID] != -1)
            nextOutbound[edgeCount] = firstOutbound[fromID];
        else
            nextOutbound[edgeCount] = -1;
        firstOutbound[fromID] = edgeCount;
        if (firstInbound != null) {
            if (firstInbound[toID] != -1)
                nextInbound[edgeCount] = firstInbound[toID];
            else
                nextInbound[edgeCount] = -1;
            firstInbound[toID] = edgeCount;
        }
        this.from[edgeCount] = fromID;
        this.to[edgeCount] = toID;
        if (capacity != 0) {
            if (this.capacity == null)
                this.capacity = new long[from.length];
            this.capacity[edgeCount] = capacity;
        }
        if (weight != 0) {
            if (this.weight == null)
                this.weight = new long[from.length];
            this.weight[edgeCount] = weight;
        }
        if (reverseEdge != -1) {
            if (this.reverseEdge == null) {
                this.reverseEdge = new int[from.length];
                Arrays.fill(this.reverseEdge, 0, edgeCount, -1);
            }
            this.reverseEdge[edgeCount] = reverseEdge;
        }
        if (edges != null)
            edges[edgeCount] = createEdge(edgeCount);
        return edgeCount++;
    }

    protected final GraphEdge createEdge(int id) {
        return new GraphEdge(id);
    }

    public final int addFlowWeightedEdge(int from, int to, long weight, long capacity) {
        if (capacity == 0) {
            return addEdge(from, to, weight, 0, -1);
        } else {
            int lastEdgeCount = edgeCount;
            addEdge(to, from, -weight, 0, lastEdgeCount + entriesPerEdge());
            return addEdge(from, to, weight, capacity, lastEdgeCount);
        }
    }

    protected int entriesPerEdge() {
        return 1;
    }

    public final int addWeightedEdge(int from, int to, long weight) {
        return addFlowWeightedEdge(from, to, weight, 0);
    }

    public final int addSimpleEdge(int from, int to) {
        return addWeightedEdge(from, to, 0);
    }

    public final int destination(int id) {
        return to[id];
    }

    protected final void initEdges() {
        if (edges == null) {
            edges = new Edge[from.length];
            for (int i = 0; i < edgeCount; i++)
                edges[i] = createEdge(i);
        }
    }

    public final boolean flag(int id, int bit) {
        return (flags[id] >> bit & 1) != 0;
    }

    public final void setFlag(int id, int bit) {
        flags[id] |= 1 << bit;
    }

    public final void removeEdge(int id) {
        setFlag(id, REMOVED_BIT);
    }

    public final boolean isRemoved(int id) {
        return flag(id, REMOVED_BIT);
    }

    public final Iterable<Edge> outbound(final int id) {
        initEdges();
        return new Iterable<Edge>() {
            public Iterator<Edge> iterator() {
                return new EdgeIterator(id, firstOutbound, nextOutbound);
            }
        };
    }

    protected void ensureEdgeCapacity(int size) {
        if (from.length < size) {
            int newSize = Math.max(size, 2 * from.length);
            if (edges != null)
                edges = resize(edges, newSize);
            from = resize(from, newSize);
            to = resize(to, newSize);
            nextOutbound = resize(nextOutbound, newSize);
            if (nextInbound != null)
                nextInbound = resize(nextInbound, newSize);
            if (weight != null)
                weight = resize(weight, newSize);
            if (capacity != null)
                capacity = resize(capacity, newSize);
            if (reverseEdge != null)
                reverseEdge = resize(reverseEdge, newSize);
            flags = resize(flags, newSize);
        }
    }

    protected final int[] resize(int[] array, int size) {
        int[] newArray = new int[size];
        System.arraycopy(array, 0, newArray, 0, array.length);
        return newArray;
    }

    private long[] resize(long[] array, int size) {
        long[] newArray = new long[size];
        System.arraycopy(array, 0, newArray, 0, array.length);
        return newArray;
    }

    private Edge[] resize(Edge[] array, int size) {
        Edge[] newArray = new Edge[size];
        System.arraycopy(array, 0, newArray, 0, array.length);
        return newArray;
    }

    protected class GraphEdge implements Edge {
        protected int id;

        protected GraphEdge(int id) {
            this.id = id;
        }

        public int getDestination() {
            return destination(id);
        }

    }

    public class EdgeIterator implements Iterator<Edge> {
        private int edgeID;
        private final int[] next;
        private int lastID = -1;

        public EdgeIterator(int id, int[] first, int[] next) {
            this.next = next;
            edgeID = nextEdge(first[id]);
        }

        private int nextEdge(int id) {
            while (id != -1 && isRemoved(id))
                id = next[id];
            return id;
        }

        public boolean hasNext() {
            return edgeID != -1;
        }

        public Edge next() {
            if (edgeID == -1)
                throw new NoSuchElementException();
            lastID = edgeID;
            edgeID = nextEdge(next[lastID]);
            return edges[lastID];
        }

        public void remove() {
            if (lastID == -1)
                throw new IllegalStateException();
            removeEdge(lastID);
            lastID = -1;
        }
    }

}

class ArrayUtils {

    public static int[] createArray(int count, int value) {
        int[] array = new int[count];
        Arrays.fill(array, value);
        return array;
    }

}

interface Edge {
    public int getDestination();
}