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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;

public class ABC0140_A3v1 {
    private static void Main(string[] args) {
        var inputs = new List<string>() {
            Console.ReadLine().Trim(),
            Console.ReadLine().Trim(),
        };

        Prepare(inputs);
    }

    private static void Prepare(List<string> inputs) {
        var numOfInts = int.Parse(inputs[0]) - 1;
        var ints = inputs[1].Split().
            Select(x => int.Parse(x)).
            ToArray();

        Compute(numOfInts, ints);
    }

    private static void Compute(int numOfInts, int[] ints) {
        var total = ints[0] + ints[numOfInts - 1];

        for (var index = 0; index < numOfInts - 1; index++) {
            total += Math.Min(ints[index], ints[index + 1]);
        }

        OutputAnswer(total.ToString());
    }

    private static void OutputAnswer(string text) => Console.WriteLine(text);
}