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: Wrong Answer)

import java.io.*;
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
	//try{
	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        OutputStream outputStream = System.out;
    	PrintWriter out = new PrintWriter(outputStream);

        int i, n, m, k;

		n = Integer.parseInt(br.readLine());
      	int[] a = new int[n-1];
      int[] dp = new int[n];
      long sum=0;
      StringTokenizer st = new StringTokenizer(br.readLine());
      for(i=0;i<n-1;i++)
      {
        a[i]=Integer.parseInt(st.nextToken());
      }
      dp[0]=a[0];
      sum+=dp[0];
      for(i=1;i<n-1;i++)
      {
        	if(a[i]>a[i-1] && a[i]>dp[i-1])
            {
              dp[i]=dp[i-1];
              sum+=dp[i];
            }
        	else
            if(a[i]<=a[i-1] && a[i]>=dp[i-1])
            {
              dp[i]=a[i];
              sum+=dp[i];
            }
        	if(a[i]<a[i-1] && a[i]<dp[i-1])
            {
              dp[i]=a[i];
              sum+=dp[i];
            }
      }
      sum+=Math.max(dp[i-1],a[i-1]);
      out.print(sum);
	out.flush();
	out.close();
	//}catch(Exception e){}
	}
}