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>

int min(int A, int B) {
	if (A >= B) {
		return B;
	} else {
		return A;
	}
}

int main(void) {
	int N;
	scanf("%d", &N);
	int i;
	int B[99];
	for(i = 0; i < N - 1; i++) {
		scanf("%d", &B[i]);
	}
	int sum = B[0];
	for(int k = 0; k <= i; k++) {
		if (k == i - 1) {
			//printf("bail! B[k] = %d\n", B[k]);
			sum += B[k];
			break;
		}
		sum += min(B[k], B[k + 1]);
		//printf("Sum is now %d\n", sum);
	}
	printf("%d", sum);
	return 0;
}