Problem:
Score : 600 points

Problem Statement

Given is an integer sequence of length N+1: A_0, A_1, A_2, \ldots, A_N. Is there a binary tree of depth N such that, for each d = 0, 1, \ldots, N, there are exactly A_d leaves at depth d? If such a tree exists, print the maximum possible number of vertices in such a tree; otherwise, print -1.

Notes

A binary tree is a rooted tree such that each vertex has at most two direct children.

A leaf in a binary tree is a vertex with zero children.

The depth of a vertex v in a binary tree is the distance from the tree's root to v. (The root has the depth of 0.)

The depth of a binary tree is the maximum depth of a vertex in the tree.

Constraints

0 \leq N \leq 10^5

0 \leq A_i \leq 10^{8} (0 \leq i \leq N)

A_N \geq 1

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_0 A_1 A_2 \cdots A_N

Output

Print the answer as an integer.

Sample Input 1

3
0 1 1 2

Sample Output 1

7

Below is the tree with the maximum possible number of vertices. It has seven vertices, so we should print 7.

Sample Input 2

4
0 0 1 0 2

Sample Output 2

10

Sample Input 3

2
0 3 1

Sample Output 3

-1

Sample Input 4

1
1 1

Sample Output 4

-1

Sample Input 5

10
0 0 1 1 2 3 5 8 13 21 34

Sample Output 5

264

Solution in Java (OpenJDK 11.0.6) (judge verdict: Accepted)


import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.Arrays;
import java.util.InputMismatchException;

/**
 * @author Mubtasim Shahriar
 */

public class Main {


	public static void main(String[] args) {

		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader sc = new InputReader(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		Solver solver = new Solver();
//		int t = sc.nextInt();
		int t = 1;
		while(t--!=0) {
			solver.solve(sc, out);
		}		
		out.close();

	}

	static class Solver {
		public void solve(InputReader sc, PrintWriter out) {
			int n = sc.nextInt()+1;
			long[] arr = sc.nextLongArray(n);
			if(arr[0]==1 && n>1) {
				out.println(-1);
				return;
			}
			if(arr[0]>1) {
				out.println(-1);
				return;
			}
			long[] fromdown = new long[n];
			long[] fromup = new long[n];
			fromdown[n-1] = arr[n-1];
			for(int i = n-2; i >= 0; i--) {
				fromdown[i] = fromdown[i+1] + arr[i];
			}
			fromup[0] = 1;
			long next = 1;
			for(int i = 1; i < n; i++) {
				long canhave = Math.min(fromdown[i], next*2);
				next = canhave - arr[i];
				fromup[i] = canhave;
				if(canhave<arr[i]) {
					out.println(-1);
					return;
				}
			}
//			out.println(Arrays.toString(fromdown));
//			out.println(Arrays.toString(fromup));
			long cnt = 0;
			for(long l : fromup) cnt += l;
				out.println(cnt);
		}
	}

	static class InputReader { 
		private boolean finished = false;

		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 peek() {
			if (numChars == -1) {
				return -1;
			}
			if (curChar >= numChars) {
				curChar = 0;
				try {
					numChars = stream.read(buf);
				} catch (IOException e) {
					return -1;
				}
				if (numChars <= 0) {
					return -1;
				}
			}
			return buf[curChar];
		}

		public int nextInt() {
			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 long nextLong() {
			int c = read();
			while (isSpaceChar(c)) {
				c = read();
			}
			int sgn = 1;
			if (c == '-') {
				sgn = -1;
				c = read();
			}
			long 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 nextString() {
			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;
		}

		private String readLine0() {
			StringBuilder buf = new StringBuilder();
			int c = read();
			while (c != '\n' && c != -1) {
				if (c != '\r') {
					buf.appendCodePoint(c);
				}
				c = read();
			}
			return buf.toString();
		}

		public String readLine() {
			String s = readLine0();
			while (s.trim().length() == 0) {
				s = readLine0();
			}
			return s;
		}

		public String readLine(boolean ignoreEmptyLines) {
			if (ignoreEmptyLines) {
				return readLine();
			} else {
				return readLine0();
			}
		}

		public BigInteger readBigInteger() {
			try {
				return new BigInteger(nextString());
			} catch (NumberFormatException e) {
				throw new InputMismatchException();
			}
		}

		public char nextCharacter() {
			int c = read();
			while (isSpaceChar(c)) {
				c = read();
			}
			return (char) c;
		}

		public double nextDouble() {
			int c = read();
			while (isSpaceChar(c)) {
				c = read();
			}
			int sgn = 1;
			if (c == '-') {
				sgn = -1;
				c = read();
			}
			double res = 0;
			while (!isSpaceChar(c) && c != '.') {
				if (c == 'e' || c == 'E') {
					return res * Math.pow(10, nextInt());
				}
				if (c < '0' || c > '9') {
					throw new InputMismatchException();
				}
				res *= 10;
				res += c - '0';
				c = read();
			}
			if (c == '.') {
				c = read();
				double m = 1;
				while (!isSpaceChar(c)) {
					if (c == 'e' || c == 'E') {
						return res * Math.pow(10, nextInt());
					}
					if (c < '0' || c > '9') {
						throw new InputMismatchException();
					}
					m /= 10;
					res += (c - '0') * m;
					c = read();
				}
			}
			return res * sgn;
		}

		public boolean isExhausted() {
			int value;
			while (isSpaceChar(value = peek()) && value != -1) {
				read();
			}
			return value == -1;
		}

		public String next() {
			return nextString();
		}

		public SpaceCharFilter getFilter() {
			return filter;
		}

		public void setFilter(SpaceCharFilter filter) {
			this.filter = filter;
		}

		public interface SpaceCharFilter {
			public boolean isSpaceChar(int ch);
		}
		public int[] nextIntArray(int n){
			int[] array=new int[n];
			for(int i=0;i<n;++i)array[i]=nextInt();
			return array;
		}
		public int[] nextSortedIntArray(int n){
			int array[]=nextIntArray(n);
			Arrays.sort(array);
			return array;
		}
		public int[] nextSumIntArray(int n){
			int[] array=new int[n];
			array[0]=nextInt();
			for(int i=1;i<n;++i)array[i]=array[i-1]+nextInt();
			return array;
		}
		public long[] nextLongArray(int n){
			long[] array=new long[n];
			for(int i=0;i<n;++i)array[i]=nextLong();
			return array;
		}
		public long[] nextSumLongArray(int n){
			long[] array=new long[n];
			array[0]=nextInt();
			for(int i=1;i<n;++i)array[i]=array[i-1]+nextInt();
			return array;
		}
		public long[] nextSortedLongArray(int n){
			long array[]=nextLongArray(n);
			Arrays.sort(array);
			return array;
		}
	}


}