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() {
	int i, N, A[101], B[101], sum = 0;
	scanf("%d", &N);
	for (i = 0; i < N - 1; i++)
		scanf("%d", &B[i]);
	B[N] = B[N - 1];
	for (i = 0; i < N - 1; i++) {
		A[0] = B[0];
		if (B[i] > B[i + 1])
			A[i + 1] = B[i + 1];
		else
			A[i + 1] = B[i];
	}
	for (i = 0; i < N; i++) {
		sum += A[i];
	}
	printf("%d", sum);
	return 0;
}