import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Collections;
import java.util.InputMismatchException;
import java.util.NoSuchElementException;
import java.util.TreeSet;

public class Main {
	public static long MOD = 1000000007;
	public static void main(String[] args) {
		IO io = new IO();
		int n = io.nextInt();
		int[] h = io.nextIntArray(n);
		Node root = makeTree(0,n,0,h);
		calc(root);
		System.out.println(root.all);
	}
	public static Node makeTree(int l,int r,int y,int[] h) {
		int min = Integer.MAX_VALUE;
		for(int i=l;i<r;i++) {
			min = Math.min(min, h[i]);
		}
		Node v = new Node(min - y, r - l);
		int nl = l;
		for(int nr=nl;nr<=r;nr++) {
			if (nr == r || h[nr] == min) {
				if (nl < nr) {
					v.children.add(makeTree(nl, nr, min, h));
				}
				nl = nr + 1;
			}
		}
		return v;
	}
	public static void calc(Node v) {
		long piChecker = 1;
		long piAllPlusChecker = 1;
		int sumWidth = 0;
		for(Node c: v.children) {
			calc(c);
			piChecker = piChecker * c.checker % MOD;
			piAllPlusChecker = piAllPlusChecker * (c.checker + c.all) % MOD;
			sumWidth += c.w;
		}
		v.checker = Mod.pow(2, v.h, MOD) * piChecker % MOD;
		v.all = Mod.pow(2, v.w - sumWidth, MOD) * piAllPlusChecker % MOD;
		v.all += (Mod.pow(2, v.h, MOD) + MOD - 2) * piChecker % MOD;
		if (v.all >= MOD) v.all -= MOD;
	}
}
class Node {
	int h,w;
	ArrayList<Node> children;
	long all,checker;
	public Node(int h, int w) {
		super();
		this.h = h;
		this.w = w;
		this.children = new ArrayList<>();
	}
	@Override
	public String toString() {
		return "(" + h + "," + w + ":" + children + ")";
	}
}
class Mod {
	public static long pow(long a,long n,long mod) {
		long res = 1;
		while(n > 0) {
			if ((n & 1) > 0) {
				res = (res * a) % mod;
			}
			a = (a * a) % mod;
			n/=2;
		}
		return res;
	}
}
class IO extends PrintWriter {
	private final InputStream in;
	private final byte[] buffer = new byte[1024];
	private int ptr = 0;
	private int buflen = 0;

	public IO() {
		this(System.in);
	}

	public IO(InputStream source) {
		super(System.out);
		this.in = source;
	}

	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 static boolean isNewLine(int c) {
		return c == '\n' || c == '\r';
	}

	public boolean hasNext() {
		while (hasNextByte() && !isPrintableChar(buffer[ptr]))
			ptr++;
		return hasNextByte();
	}

	public boolean hasNextLine() {
		while (hasNextByte() && isNewLine(buffer[ptr]))
			ptr++;
		return hasNextByte();
	}

	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 char[] nextCharArray(int len) {
		if (!hasNext()) {
			throw new NoSuchElementException();
		}
		char[] s = new char[len];
		int i = 0;
		int b = readByte();
		while (isPrintableChar(b)) {
			if (i == len) {
				throw new InputMismatchException();
			}
			s[i++] = (char) b;
			b = readByte();
		}
		return s;
	}

	public String nextLine() {
		if (!hasNextLine()) {
			throw new NoSuchElementException();
		}
		StringBuilder sb = new StringBuilder();
		int b = readByte();
		while (!isNewLine(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();
		}
	}

	public int nextInt() {
		long nl = nextLong();
		if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) {
			throw new NumberFormatException();
		}
		return (int) nl;
	}

	public char nextChar() {
		if (!hasNext()) {
			throw new NoSuchElementException();
		}
		return (char) readByte();
	}

	public double nextDouble() {
		return Double.parseDouble(next());
	}

	public int[] nextIntArray(int n) {
		int[] a = new int[n];
		for (int i = 0; i < n; i++)
			a[i] = nextInt();
		return a;
	}

	public long[] nextLongArray(int n) {
		long[] a = new long[n];
		for (int i = 0; i < n; i++)
			a[i] = nextLong();
		return a;
	}

	public double[] nextDoubleArray(int n) {
		double[] a = new double[n];
		for (int i = 0; i < n; i++)
			a[i] = nextDouble();
		return a;
	}

	public void nextIntArrays(int[]... a) {
		for (int i = 0; i < a[0].length; i++)
			for (int j = 0; j < a.length; j++)
				a[j][i] = nextInt();
	}

	public int[][] nextIntMatrix(int n, int m) {
		int[][] a = new int[n][];
		for (int i = 0; i < n; i++)
			a[i] = nextIntArray(m);
		return a;
	}

	public char[][] nextCharMap(int n, int m) {
		char[][] a = new char[n][];
		for (int i = 0; i < n; i++)
			a[i] = nextCharArray(m);
		return a;
	}

	public void close() {
		super.close();
		try {
			in.close();
		} catch (IOException e) {
		}
	}
}


Measured memory_bytes: 22996