Problem:
Score : 1000 points

Problem Statement

There is a stack of N cards, each of which has a non-negative integer written on it. The integer written on the i-th card from the top is A_i.

Snuke will repeat the following operation until two cards remain:

Choose three consecutive cards from the stack.

Eat the middle card of the three.

For each of the other two cards, replace the integer written on it by the sum of that integer and the integer written on the card eaten.

Return the two cards to the original position in the stack, without swapping them.

Find the minimum possible sum of the integers written on the last two cards remaining.

Constraints

2 \leq N \leq 18

0 \leq A_i \leq 10^9 (1\leq i\leq N)

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_1 A_2 ... A_N

Output

Print the minimum possible sum of the integers written on the last two cards remaining.

Sample Input 1

4
3 1 4 2

Sample Output 1

16

We can minimize the sum of the integers written on the last two cards remaining by doing as follows:

Initially, the integers written on the cards are 3, 1, 4, and 2 from top to bottom.

Choose the first, second, and third card from the top. Eat the second card with 1 written on it, add 1 to each of the other two cards, and return them to the original position in the stack. The integers written on the cards are now 4, 5, and 2 from top to bottom.

Choose the first, second, and third card from the top. Eat the second card with 5 written on it, add 5 to each of the other two cards, and return them to the original position in the stack. The integers written on the cards are now 9 and 7 from top to bottom.

The sum of the integers written on the last two cards remaining is 16.

Sample Input 2

6
5 2 4 1 6 9

Sample Output 2

51

Sample Input 3

10
3 1 4 1 5 9 2 6 5 3

Sample Output 3

115

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Arrays;
import java.io.IOException;
import java.io.UncheckedIOException;
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 << 27);
        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);
            DAddAndRemove solver = new DAddAndRemove();
            solver.solve(1, in, out);
            out.close();
        }
    }

    static class DAddAndRemove {
        int n;
        long[] a;
        LongHashMap[][] dp;

        public long dp(int l, int r, int x, int y) {
            if (l + 1 >= r) {
                return 0;
            }
            long key = DigitUtils.asLong(x, y);
            long ans;
            if ((ans = dp[l][r].getOrDefault(key, -1)) == -1) {
                ans = (long) 1e18;
                for (int i = l + 1; i < r; i++) {
                    ans = Math.min(ans,
                            dp(l, i, x, x + y) + dp(i, r, x + y, y) +
                                    a[i] * (x + y));
                }
                dp[l][r].put(key, ans);
            }
            return ans;
        }

        public void solve(int testNumber, FastInput in, FastOutput out) {
            n = in.readInt();
            a = new long[n];
            for (int i = 0; i < n; i++) {
                a[i] = in.readInt();
            }

            dp = new LongHashMap[n][n];
            for (int i = 0; i < n; i++) {
                for (int j = i + 2; j < n; j++) {
                    dp[i][j] = new LongHashMap(1 << (n - 1), false);
                }
            }

            long ans = dp(0, n - 1, 1, 1) + a[0] + a[n - 1];

            out.println(ans);
        }

    }

    static class DigitUtils {
        private static long mask32 = (1L << 32) - 1;

        private DigitUtils() {
        }

        public static long asLong(int high, int low) {
            return (((long) high) << 32) | (((long) low) & mask32);
        }

    }

    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(long c) {
            cache.append(c);
            return this;
        }

        public FastOutput println(long 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();
        }

    }

    static class LongHashMap {
        private int[] slot;
        private int[] next;
        private long[] keys;
        private long[] values;
        private int alloc;
        private boolean[] removed;
        private int mask;
        private int size;
        private boolean rehash;
        private Hasher hasher = new Hasher();

        public LongHashMap(int cap, boolean rehash) {
            this.mask = (1 << (32 - Integer.numberOfLeadingZeros(cap - 1))) - 1;
            slot = new int[mask + 1];
            next = new int[cap + 1];
            keys = new long[cap + 1];
            values = new long[cap + 1];
            removed = new boolean[cap + 1];
            this.rehash = rehash;
        }

        private void doubleCapacity() {
            int newSize = Math.max(next.length + 10, next.length * 2);
            next = Arrays.copyOf(next, newSize);
            keys = Arrays.copyOf(keys, newSize);
            values = Arrays.copyOf(values, newSize);
            removed = Arrays.copyOf(removed, newSize);
        }

        public void alloc() {
            alloc++;
            if (alloc >= next.length) {
                doubleCapacity();
            }
            next[alloc] = 0;
            removed[alloc] = false;
            size++;
        }

        private void rehash() {
            int[] newSlots = new int[Math.max(16, slot.length * 2)];
            int newMask = newSlots.length - 1;
            for (int i = 0; i < slot.length; i++) {
                if (slot[i] == 0) {
                    continue;
                }
                int head = slot[i];
                while (head != 0) {
                    int n = next[head];
                    int s = hash(keys[head]) & newMask;
                    next[head] = newSlots[s];
                    newSlots[s] = head;
                    head = n;
                }
            }
            this.slot = newSlots;
            this.mask = newMask;
        }

        private int hash(long x) {
            return hasher.hash(x);
        }

        public void put(long x, long y) {
            put(x, y, true);
        }

        public void put(long x, long y, boolean cover) {
            int h = hash(x);
            int s = h & mask;
            if (slot[s] == 0) {
                alloc();
                slot[s] = alloc;
                keys[alloc] = x;
                values[alloc] = y;
            } else {
                int index = findIndexOrLastEntry(s, x);
                if (keys[index] != x) {
                    alloc();
                    next[index] = alloc;
                    keys[alloc] = x;
                    values[alloc] = y;
                } else if (cover) {
                    values[index] = y;
                }
            }
            if (rehash && size >= slot.length) {
                rehash();
            }
        }

        public long getOrDefault(long x, long def) {
            int h = hash(x);
            int s = h & mask;
            if (slot[s] == 0) {
                return def;
            }
            int index = findIndexOrLastEntry(s, x);
            return keys[index] == x ? values[index] : def;
        }

        private int findIndexOrLastEntry(int s, long x) {
            int iter = slot[s];
            while (keys[iter] != x) {
                if (next[iter] != 0) {
                    iter = next[iter];
                } else {
                    return iter;
                }
            }
            return iter;
        }

        public LongEntryIterator iterator() {
            return new LongEntryIterator() {
                int index = 1;
                int readIndex = -1;


                public boolean hasNext() {
                    while (index <= alloc && removed[index]) {
                        index++;
                    }
                    return index <= alloc;
                }


                public long getEntryKey() {
                    return keys[readIndex];
                }


                public long getEntryValue() {
                    return values[readIndex];
                }


                public void next() {
                    if (!hasNext()) {
                        throw new IllegalStateException();
                    }
                    readIndex = index;
                    index++;
                }
            };
        }

        public String toString() {
            LongEntryIterator iterator = iterator();
            StringBuilder builder = new StringBuilder("{");
            while (iterator.hasNext()) {
                iterator.next();
                builder.append(iterator.getEntryKey()).append("->").append(iterator.getEntryValue()).append(',');
            }
            if (builder.charAt(builder.length() - 1) == ',') {
                builder.setLength(builder.length() - 1);
            }
            builder.append('}');
            return builder.toString();
        }

    }

    static interface LongEntryIterator {
        boolean hasNext();

        void next();

        long getEntryKey();

        long getEntryValue();

    }

    static class FastInput {
        private final InputStream is;
        private byte[] buf = new byte[1 << 20];
        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;
        }

    }

    static class Hasher {
        private long time = System.nanoTime() + System.currentTimeMillis();

        private int shuffle(long x) {
            x += time;
            x += 0x9e3779b97f4a7c15L;
            x = (x ^ (x >>> 30)) * 0xbf58476d1ce4e5b9L;
            x = (x ^ (x >>> 27)) * 0x94d049bb133111ebL;
            return (int) (x ^ (x >>> 31));
        }

        public int hash(long x) {
            return shuffle(x);
        }

    }
}