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 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<stdio.h>
#include<stdlib.h>


/*ex)
 * 3
 * 2 5
 * (2,2,5)
 * */
int main() {
	/*
	 参加者N人
	 */
	/*変数宣言*/
	int N;

	/*変数受け取り*/
	scanf("%d", &N);

	int b[100];
	for (int i = 0; i < N-1; i++) {
		scanf("%d", &b[i]);
	}


	int a[100];
	/*配列aに末尾から格納*/
	for (int i = N-1; i >= 0; i--) {
		//最初はそのままb[n-1]をa[n]へ
		if(i == N-1){
			a[i] = b[i-1];
		}

		/*二回目以降
		 * 前の値＜後ろの値なら
		 * 前の値をaに格納
		 *
		 * それ以外なら
		 * 後ろの値をaに格納
		 * */
		if(b[i] > b[i-1]){
			a[i] = b[i-1];
		}
		else{
			a[i] = b[i];
		}
	}

	int ans = 0;

	for (int i = 0; i < N; ++i) {
		ans += a[i];
	}

	printf("%d\n",ans);
	return 0;
}