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 (Clang 3.8.0) (judge verdict: Accepted)

#include <stdio.h>
#include <string.h>
#include <math.h>
int main(void){
    
    int n;
    int a[999]={};
    int b[999]={};
    int ans=0;
    int tmp=0;
    
    scanf("%d", &n);
    
    for(int i=1; i<n; i++){
        
        scanf("%d", &b[i]);
        
    }
    
    for(int i=1; i<=n; i++){
        
        a[i] = 999999;
        
    }
    
    for(int i=1; i<n; i++){
        
        if(a[i]>b[i]){
            
            a[i] = b[i];
            
        }
        
        if(a[i+1]>b[i]){
            
            a[i+1] = b[i];
            
        }
        
    }
    
    for(int i=1; i<=n; i++){
        
        ans += a[i];
        
    }
    
    printf("%d", ans);
    
    return 0;
    
}