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 = new int[N-1];
      for(int i=0; i<N - 1; i++){ B[i] = sc.nextInt();}
      int[] A = new int[N];
      for(int i=0; i<N; i++){ A[i] = 100001;}
      int ans=0;
      
      for(int i=0; i<N-1; i++){
      	int n = B[i];
        if(A[i]>n) A[i]=n;
        if(A[i+1]>n) A[i+1]=n;
      }
      for(int i=0; i<N; i++)
        ans += A[i];
      
      System.out.println(ans);

	}
}