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.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.StringTokenizer;
import java.io.IOException;
import java.io.BufferedReader;
import java.util.Comparator;
import java.io.InputStreamReader;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author Washoum
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        inputClass in = new inputClass(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        CMaximalValue solver = new CMaximalValue();
        solver.solve(1, in, out);
        out.close();
    }

    static class CMaximalValue {
        public void solve(int testNumber, inputClass sc, PrintWriter out) {
            int n = sc.nextInt();
            CMaximalValue.Pair[] a = new CMaximalValue.Pair[n - 1];
            for (int i = 0; i < n - 1; i++) {
                a[i] = new CMaximalValue.Pair(sc.nextInt(), i);
            }
            int[] ans = new int[n];
            Arrays.fill(ans, -1);
            Arrays.sort(a, Comparator.comparingInt(a2 -> a2.x));
            for (int i = 0; i < n - 1; i++) {
                if (ans[a[i].y] == -1) {
                    ans[a[i].y] = a[i].x;
                }
                if (ans[a[i].y + 1] == -1) {
                    ans[a[i].y + 1] = a[i].x;
                }
            }
            long sum = 0;
            for (int i = 0; i < n; i++) {
                sum += ans[i];
            }
            out.println(sum);
        }

        static class Pair {
            int x;
            int y;

            public Pair(int x, int y) {
                this.x = x;
                this.y = y;
            }

        }

    }

    static class inputClass {
        BufferedReader br;
        StringTokenizer st;

        public inputClass(InputStream in) {

            br = new BufferedReader(new InputStreamReader(in));
        }

        public String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

    }
}