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 main(void)
{
    int N;
    int B[99];
    int A[100];
    int i;
    int sum;
    
    scanf("%d", &N);
    if(N<=100)
    {
        for(i=0;i<N-1;i++)
        {
            scanf("%d",&B[i]);
        }
    }
    
    sum = B[0];
    for(i=0; i<N-2; i++)    
    {
        if(B[i]<=B[i+1])
        {
            sum = sum + B[i];
        }
        else
        {
            sum = sum + B[i+1];
        }
    }
    sum = sum + B[N-2];
    printf("%d",sum);
    return(0);
}