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 min_2(int a, int b) {
	if (a <= b) return a;
	else return b;
}

int main() {
	int N;
	scanf("%d",&N);
	int B[N];
	for (int i = 0; i < N-1; i++) {
		scanf("%d",&B[i]);
	}
	int sum = 0;
	for (int i = 0; i < N-1; i++) {
		int tmp;
		if (i != N-2) {
			tmp = min_2(B[i], B[i+1]);
			sum += tmp;
			if (i == 0) sum += tmp;
		}
		else sum += B[i];
	}
	if (N == 2) sum += B[0];
	printf("%d\n", sum);
	return 0;
}