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 (Clang 3.8.0) (judge verdict: Wrong Answer)

#include <stdio.h>

int		max(int a, int b)
{
	if (a < b)
		return b;
	return a;
}

int main()
{
	int N;
	scanf("%d", &N);
	int i = 0;
	int b[N];
	int sum = 0;
	while (i < N - 1)
		scanf("%d", &b[i++]);
	sum = b[0];
	i = 1;
	while (i < N - 1)
	{
		if (b[i] > b[i + 1])
			sum += b[i - 1];
		else if (b[i] <= b[i + 1])
			sum += b[i];
		i++;
	}
	sum += b[N - 2];
	printf("%d\n", sum);
	return 0;
}