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;

namespace A
{
    class Program
    {
        static void Main(string[] args)
        {
            var N = Io.Read<int>();
            var Blist = Io.ReadList<int>();

            var output = Blist[0];
            for (var i = 0; i < N - 2; i++)
            {
                output += Math.Min(Blist[i], Blist[i + 1]);
            }

            output += Blist[N - 2];

            Io.Write(output.ToString());
        }
    }

    class Io
    {
        public static string Read()
        {
            return Console.ReadLine();
        }

        public static IEnumerable<string> ReadRepeat(int count)
        {
            return Enumerable.Range(0, count).Select(_ => Read());
        }

        public static T Read<T>()
        {
            return (T)Convert.ChangeType(Read(), typeof(T));
        }

        public static IEnumerable<T> ReadRepeat<T>(int count)
        {
            return Enumerable.Range(0, count).Select(_ => Read<T>());
        }

        public static string[] ReadList(char devide = ' ')
        {
            return Read().Split(devide);
        }

        public static T[] ReadList<T>(char devide = ' ')
        {
            return ReadList(devide)
                .Select(s => (T)Convert.ChangeType(s, typeof(T)))
                .ToArray();
        }

        public static IEnumerable<T[]> ReadListRepeat<T>(int count, char devide = ' ')
        {
            return Enumerable.Range(0, count).Select(_ => ReadList<T>(devide));
        }

        public static void Write(string value)
        {
            Console.WriteLine(value);
        }
    }
}