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.*;
class Main{
  public static void main(String[] args){
    Scanner scan=new Scanner(System.in);
    int N=scan.nextInt();
    int[] A=new int[N];
    int[] B=new int[N-1];
    int ans=0;
    for(int i=0;i<N-1;i++){
      B[i]=scan.nextInt();
    }
    A[0]=B[0];
    for(int i=0;i<N-2;i++){
      if(B[i]<B[i+1]){
        A[i+1]=B[i];
      }else{
        A[i+1]=B[i+1];
      }
    }
    A[N-1]=B[N-2];
    for(int i=0;i<N;i++){
      ans+=A[i];
    }
    System.out.println(ans);
  }
}