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>
#define MAX (int)1e5

int min(int a, int b){
  return a<b ? a : b;
}

int main(){
  int n,b[MAX],i,sum=0;
  
  scanf("%d",&n);
  for(i=0;i<n-1;i++)
    scanf("%d",&b[i]);
  
  sum += b[0];
  for(i=0;i<n-2;i++)
    sum += min(b[i],b[i+1]);
  sum += b[n-2];
  
  printf("%d\n",sum);
  return 0;
}