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 9.2.1) (judge verdict: Accepted)

#include<stdio.h>
#include<string.h>

#define MAX(a, b) (((a)>(b)) ? (a) : (b))
#define MIN(a, b) (((a)<(b)) ? (a) : (b))

int main()
{
    int n;
    int array_a[101];
    int array_b[101];
    long long int a = 0;

    scanf("%d", &n);

    for (int i = 1; i<n; i++)
    {
        scanf("%d", &array_b[i]);
        array_a[i] = 0;
    }

    a += array_b[1];

    for (int i = 2; i<n; i++)
    {
        a += MIN(array_b[i], array_b[i-1]);
    }

    a += array_b[n-1];

    printf("%lld", a);

    return 0;
}