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>

void gyoretu(int *a, int *b, int n){
    a[0] = b[0];
    int i;

    for(i = 1; b[i]; i++){
        if(b[i - 1] < b[i]){
            a[i] = b[i - 1];
        }
        else{
            a[i] = b[i];
        }
    }
    a[n - 1] = b[n - 2];
}

int suma(int *a, int n){
    int tmp = 0;
    int i;

    for(i = 0; i < n; i++){
        tmp += a[i];
    }

    return tmp;
}

int main(void){
    int n;
    int a[100] = {0};
    int b[100] = {0};
    int i;

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

    gyoretu(a, b, n);

    printf("%d", suma(a, n));
}