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: Accepted)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#define max(a, b)	(((a) > (b)) ? (a) : (b))		/* ２個の値の最大値 */
#define min(a, b)	(((a) < (b)) ? (a) : (b))		/* ２個の値の最小値 */
#define ENTER		printf("\n")					/* 改行プリント */
int DBG = 0;										/* デバッグプリント 提出時は0 */
/* main *************************************************************/
int main()
{
	int		a,b[101],c,i,j,k,n,m,x,y,ans = 0;
	char	str[256];
	
	scanf("%d", &n);
	for(i=1;i<n;i++) scanf("%d", &b[i]);
	b[0] = b[1];
	b[n] = 0x7fffffff;
	if (DBG) {
		for(i=0;i<n;i++) printf("%d ",b[i]);
		ENTER;
	}
	for(i=0;i<n;i++) {
		if (b[i] > b[i+1]) b[i] = b[i+1];
		ans += b[i];
	}
	if (DBG) {
		for(i=0;i<n;i++) printf("%d ",b[i]);
		ENTER;
	}
	printf("%d\n",ans);


	return 0;
}