Problem:
Score : 300 points

Problem Statement

There is an integer sequence A of length N whose values are unknown.

Given is an integer sequence B of length N-1 which is known to satisfy the following:

B_i \geq \max(A_i, A_{i+1})

Find the maximum possible sum of the elements of A.

Constraints

All values in input are integers.

2 \leq N \leq 100

0 \leq B_i \leq 10^5

Input

Input is given from Standard Input in the following format:

N
B_1 B_2 ... B_{N-1}

Output

Print the maximum possible sum of the elements of A.

Sample Input 1

3
2 5

Sample Output 1

9

A can be, for example, ( 2 , 1 , 5 ), ( -1 , -2 , -3 ), or ( 2 , 2 , 5 ). Among those candidates, A = ( 2 , 2 , 5 ) has the maximum possible sum.

Sample Input 2

2
3

Sample Output 2

6

Sample Input 3

6
0 153 10 10 23

Sample Output 3

53

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

import java.util.*;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] b = arrayInt(sc, n - 1);
		sc.close();
		int[] a = new int[n];
		int sum = 0;
		a[0] = b[0];
		for (int i = 0; i < n - 1; i++) {
			if (a[i] > b[i]) {
				a[i] = b[i];
			}
			a[i + 1] = b[i];
			sum += a[i];
		}
		sum += a[n - 1];
		System.out.println(sum);
	}

	public static long modFactorial(long n, long mod) {
		long ans = 1;
		for (int i = 1; i <= n; i++) {
			ans *= i;
			ans %= mod;
		}
		return ans;
	}

	public static int arrayMax(int[] array) {
		int ans = Integer.MIN_VALUE;
		for (int i = 0; i < array.length; i++) {
			if (array[i] > ans)
				ans = array[i];
		}
		return ans;
	}

	public static int[] arrayInt(Scanner sc, int n) {
		int[] array = new int[n];
		for (int i = 0; i < n; i++) {
			array[i] = sc.nextInt();
		}
		return array;
	}

	public static long[] arrayLong(Scanner sc, int n) {
		long[] array = new long[n];
		for (int i = 0; i < n; i++) {
			array[i] = sc.nextLong();
		}
		return array;
	}

	public static double[] arrayDouble(Scanner sc, int n) {
		double[] array = new double[n];
		for (int i = 0; i < n; i++) {
			array[i] = sc.nextDouble();
		}
		return array;
	}
}

class Combination {
	static final int MOD = 1000000007;
	long[] fac;
	long[] finv;
	long[] inv;

	public Combination(int size) {
		fac = new long[size];
		finv = new long[size];
		inv = new long[size];
		fac[0] = 1;
		fac[1] = 1;
		finv[0] = 1;
		finv[1] = 1;
		inv[1] = 1;
		for (int i = 2; i < size; i++) {
			fac[i] = fac[i - 1] * i % MOD;
			inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
			finv[i] = finv[i - 1] * inv[i] % MOD;
		}
	}

	public long getComb(int n, int k) {
		if (n < k || n < 0 || k < 0) {
			return 0;
		}
		return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
	}
}