You are given a string S of length 2N, containing N occurrences of `a` and N occurrences of `b`.

You will choose some of the characters in S. Here, for each i = 1,2,...,N, it is not allowed to choose exactly one of the following two: the i-th occurrence of `a` and the i-th occurrence of `b`. (That is, you can only choose both or neither.) Then, you will concatenate the chosen characters (without changing the order).

Find the lexicographically largest string that can be obtained in this way.

Constraints

* 1 \leq N \leq 3000
* S is a string of length 2N containing N occurrences of `a` and N occurrences of `b`.

Input

Input is given from Standard Input in the following format:


N
S


Output

Print the lexicographically largest string that satisfies the condition.

Examples

Input

3
aababb


Output

abab


Input

3
bbabaa


Output

bbabaa


Input

6
bbbaabbabaaa


Output

bbbabaaa


Input

9
abbbaababaababbaba


Output

bbaababababa
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintStream;
import java.util.Arrays;
import java.util.Collection;
import java.io.IOException;
import java.util.stream.Collectors;
import java.util.ArrayList;
import java.io.UncheckedIOException;
import java.util.List;
import java.util.stream.Stream;
import java.io.Closeable;
import java.io.Writer;
import java.io.OutputStreamWriter;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) throws Exception {
        Thread thread = new Thread(null, new TaskAdapter(), "", 1 << 29);
        thread.start();
        thread.join();
    }

    static class TaskAdapter implements Runnable {
        @Override
        public void run() {
            InputStream inputStream = System.in;
            OutputStream outputStream = System.out;
            FastInput in = new FastInput(inputStream);
            FastOutput out = new FastOutput(outputStream);
            ESynchronizedSubsequence solver = new ESynchronizedSubsequence();
            solver.solve(1, in, out);
            out.close();
        }
    }

    static class ESynchronizedSubsequence {
        Debug debug = new Debug(false);

        public void solve(int testNumber, FastInput in, FastOutput out) {
            int n = in.readInt();
            int[] s = new int[n * 2];
            for (int i = 0; i < 2 * n; i++) {
                s[i] = in.readChar() - 'a';
            }
            List<Block> blocks = new ArrayList<>(n);
            int cur = 0;
            int left = 0;
            for (int i = 0; i < 2 * n; i++) {
                if (s[i] == 0) {
                    cur--;
                } else {
                    cur++;
                }
                if (cur == 0) {
                    Block b = new Block();
                    b.start = s[left];
                    b.data = Arrays.copyOfRange(s, left, i + 1);
                    left = i + 1;
                    if (b.start == 0) {
                        extractType0(b);
                    } else {
                        extractType1(b);
                    }
                    blocks.add(b);
                }
            }
            debug.debug("blocks", blocks);

            List<Block> type1 = blocks.stream().filter(x -> x.start == 1).collect(Collectors.toList());
            for (int i = 0; i < type1.size(); i++) {
                type1.get(i).index = i;
            }
            type1.sort((a, b) -> {
                int ans = -a.seq.compareTo(b.seq);
                if (ans == 0) {
                    ans = a.index - b.index;
                }
                return ans;
            });

            StringBuilder ans = new StringBuilder();
            int now = 0;
            for (Block b : type1) {
                if (b.index < now) {
                    continue;
                }
                ans.append(b.seq);
                now = b.index + 1;
            }
            int tail = blocks.size();
            while (tail > 0 && blocks.get(tail - 1).start == 0) {
                tail--;
            }
            for (int i = tail; i < blocks.size(); i++) {
                ans.append(blocks.get(i).seq);
            }
            for (int i = 0; i < ans.length(); i++) {
                ans.setCharAt(i, (char) (ans.charAt(i) - '0' + 'a'));
            }
            out.println(ans.toString());
        }

        public String build(int[] data, boolean[] added) {
            StringBuilder builder = new StringBuilder(data.length);
            for (int i = 0; i < data.length; i++) {
                if (added[i]) {
                    builder.append(data[i]);
                }
            }
            return builder.toString();
        }

        public int[][] getIndices(int[] data) {
            int[][] indices = new int[2][data.length / 2];
            int[] wpos = new int[2];
            for (int i = 0; i < data.length; i++) {
                indices[data[i]][wpos[data[i]]++] = i;
            }
            return indices;
        }

        public void extractType0(Block b) {
            int[] data = b.data;
            int[][] indices = getIndices(data);
            StringBuilder ans = new StringBuilder(data.length);
            int cur = 0;
            for (int i = 0; i < data.length / 2; i++) {
                if (cur <= indices[0][i]) {
                    ans.append("01");
                    cur = indices[1][i] + 1;
                }
            }
            b.seq = ans.toString();
        }

        public String max(String a, String b) {
            return a.compareTo(b) >= 0 ? a : b;
        }

        public void extractType1(Block b) {
            int[] data = b.data;
            int[][] indices = getIndices(data);
            boolean[] added = new boolean[data.length];
            Arrays.fill(added, true);
            String s = build(data, added);
            for (int i = 0; i < data.length / 2; i++) {
                added[indices[0][i]] = added[indices[1][i]] = false;
                String cur = build(data, added);
                s = max(s, cur);
            }
            b.seq = s;
        }

    }

    static class Block {
        int start;
        int[] data;
        int index;
        String seq;

        public String toString() {
            return seq;
        }

    }

    static class FastInput {
        private final InputStream is;
        private byte[] buf = new byte[1 << 13];
        private int bufLen;
        private int bufOffset;
        private int next;

        public FastInput(InputStream is) {
            this.is = is;
        }

        private int read() {
            while (bufLen == bufOffset) {
                bufOffset = 0;
                try {
                    bufLen = is.read(buf);
                } catch (IOException e) {
                    bufLen = -1;
                }
                if (bufLen == -1) {
                    return -1;
                }
            }
            return buf[bufOffset++];
        }

        public void skipBlank() {
            while (next >= 0 && next <= 32) {
                next = read();
            }
        }

        public int readInt() {
            int sign = 1;

            skipBlank();
            if (next == '+' || next == '-') {
                sign = next == '+' ? 1 : -1;
                next = read();
            }

            int val = 0;
            if (sign == 1) {
                while (next >= '0' && next <= '9') {
                    val = val * 10 + next - '0';
                    next = read();
                }
            } else {
                while (next >= '0' && next <= '9') {
                    val = val * 10 - next + '0';
                    next = read();
                }
            }

            return val;
        }

        public char readChar() {
            skipBlank();
            char c = (char) next;
            next = read();
            return c;
        }

    }

    static class Debug {
        private boolean offline;
        private PrintStream out = System.err;
        static int[] empty = new int[0];

        public Debug(boolean enable) {
            offline = enable && System.getSecurityManager() == null;
        }

        public Debug debug(String name, Object x) {
            return debug(name, x, empty);
        }

        public Debug debug(String name, Object x, int... indexes) {
            if (offline) {
                if (x == null || !x.getClass().isArray()) {
                    out.append(name);
                    for (int i : indexes) {
                        out.printf("[%d]", i);
                    }
                    out.append("=").append("" + x);
                    out.println();
                } else {
                    indexes = Arrays.copyOf(indexes, indexes.length + 1);
                    if (x instanceof byte[]) {
                        byte[] arr = (byte[]) x;
                        for (int i = 0; i < arr.length; i++) {
                            indexes[indexes.length - 1] = i;
                            debug(name, arr[i], indexes);
                        }
                    } else if (x instanceof short[]) {
                        short[] arr = (short[]) x;
                        for (int i = 0; i < arr.length; i++) {
                            indexes[indexes.length - 1] = i;
                            debug(name, arr[i], indexes);
                        }
                    } else if (x instanceof boolean[]) {
                        boolean[] arr = (boolean[]) x;
                        for (int i = 0; i < arr.length; i++) {
                            indexes[indexes.length - 1] = i;
                            debug(name, arr[i], indexes);
                        }
                    } else if (x instanceof char[]) {
                        char[] arr = (char[]) x;
                        for (int i = 0; i < arr.length; i++) {
                            indexes[indexes.length - 1] = i;
                            debug(name, arr[i], indexes);
                        }
                    } else if (x instanceof int[]) {
                        int[] arr = (int[]) x;
                        for (int i = 0; i < arr.length; i++) {
                            indexes[indexes.length - 1] = i;
                            debug(name, arr[i], indexes);
                        }
                    } else if (x instanceof float[]) {
                        float[] arr = (float[]) x;
                        for (int i = 0; i < arr.length; i++) {
                            indexes[indexes.length - 1] = i;
                            debug(name, arr[i], indexes);
                        }
                    } else if (x instanceof double[]) {
                        double[] arr = (double[]) x;
                        for (int i = 0; i < arr.length; i++) {
                            indexes[indexes.length - 1] = i;
                            debug(name, arr[i], indexes);
                        }
                    } else if (x instanceof long[]) {
                        long[] arr = (long[]) x;
                        for (int i = 0; i < arr.length; i++) {
                            indexes[indexes.length - 1] = i;
                            debug(name, arr[i], indexes);
                        }
                    } else {
                        Object[] arr = (Object[]) x;
                        for (int i = 0; i < arr.length; i++) {
                            indexes[indexes.length - 1] = i;
                            debug(name, arr[i], indexes);
                        }
                    }
                }
            }
            return this;
        }

    }

    static class FastOutput implements AutoCloseable, Closeable, Appendable {
        private StringBuilder cache = new StringBuilder(10 << 20);
        private final Writer os;

        public FastOutput append(CharSequence csq) {
            cache.append(csq);
            return this;
        }

        public FastOutput append(CharSequence csq, int start, int end) {
            cache.append(csq, start, end);
            return this;
        }

        public FastOutput(Writer os) {
            this.os = os;
        }

        public FastOutput(OutputStream os) {
            this(new OutputStreamWriter(os));
        }

        public FastOutput append(char c) {
            cache.append(c);
            return this;
        }

        public FastOutput append(String c) {
            cache.append(c);
            return this;
        }

        public FastOutput println(String c) {
            return append(c).println();
        }

        public FastOutput println() {
            cache.append(System.lineSeparator());
            return this;
        }

        public FastOutput flush() {
            try {
                os.append(cache);
                os.flush();
                cache.setLength(0);
            } catch (IOException e) {
                throw new UncheckedIOException(e);
            }
            return this;
        }

        public void close() {
            flush();
            try {
                os.close();
            } catch (IOException e) {
                throw new UncheckedIOException(e);
            }
        }

        public String toString() {
            return cache.toString();
        }

    }
}

