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>

int main(void)
{
	int N;
	int i;

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

	A[0]=B[0];
	A[N-1]=B[N-2];	
	for(i=0;i<N-1;i++){
		if(B[i]<B[i+1]){
			A[i+1]=B[i];
			i++;
		}
	}
	int cnt=0;
	for(i=0;i<N;i++){
		cnt+=A[i];
	}
	printf("%d\n",cnt);

	return 0;
}