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){
    // Your code here!
    int N, A[100], B[99];
    long sum = 0;
    scanf("%d",&N);
    
    for(int i = 0; i < N-1; i++)
    {
        scanf("%d",&B[i]);
    }
    
    for(int i = 0; i < N-1; i = i + 2)
    {
        A[i] = B[i];
        A[i+1] = B[i];
    }
    if((N-2)%2 == 1)
        A[N-1] = B[N-2];
        
    for(int i = 1; i < N-1; i = i + 2)
    {
        if(A[i] > B[i])
            A[i] = B[i];
            
        if(A[i+1] > B[i])
            A[i+1] = B[i];
    }
    
    for(int i = 0; i < N; i++)
    {
        //printf("%d ", A[i]);
        sum += A[i];
    }
    //printf("\n");
    
    
    printf("%ld\n",sum);
}