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>
#include <stdlib.h>

int min(int x, int y){
    return x < y ? x : y;
}
int main(void){
    int N;

    scanf("%d", &N);

    int i;

    int *B = (int *) malloc(sizeof(int) * (N - 1));

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

    for(i = 1; i < N - 1; i ++){
        sum += min(B[i - 1], B[i]);
    }
    sum += B[N - 2];

    printf("%d\n", sum);
}