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)

//Twitter@KonoLv1 2020年春卒で現在就職活動中！
 
#include <stdio.h>
#include <math.h>
#include <string.h>
#include <stdlib.h>
 
int main(void){
    int i,j;            //  ループ文に使用
    int x,y,z;
    int count1,count2,count;   //  カウント用に使用
    int box[256] = {};
    int box2[256] = {};
    int box3[256] = {};
    char s[200001] = {};        //  文字列
    char s2[200001] = {};        //  文字列
    int a,b,c,n,save;
    a = b = c = i = 0;
    save = -999;
    int mode = 0;
    count = count1 = count2 = 0;
 
    //  入力処理
    
    scanf("%d",&n);
            
    for (i = 0; i < n - 1; i++){
        scanf("%d",&box[i]);
    }
    
    box2[0] = box[0];
    
    for (i = 1; i < n - 1 ; i++){
        if (box[i] > box[i - 1]){
            box2[i] = box[i - 1];
        }else{
            box2[i] = box[i];
        }
    }
    
    box2[n - 1] = box[n - 2];
            
        
     
        
    
    //  計算処理

    for (i = 0; i < n; i++){
        count = count + box2[i];
    }
  
    //  出力処理

    printf("%d",count);

 
}