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: Wrong Answer)

#include<stdio.h>
#define min(a,b) (a)<(b)?(a):(b)
#define max(a,b) (a)>(b)?(a):(b)
int main(void)
{
  int n;
  int b[100],left,mid,right;
  long long ans=0;
  scanf("%d",&n);
  for(int i=0;i<n-1;i++){
    scanf("%d",&b[i]);
  }
  left=b[0];
  mid=b[0];
  right=b[1];
  for(int i=0;i<n;i++){
    if(i<n-2){
      mid=b[i];
      right=b[i+1];
      //printf("left=%d mid=%d right=%d ans+=%lld\n",left,mid,right,ans);
      ans+=min(min(left,mid),right);
      left=mid;
      mid=right;
    }else if(i==n-2){
      /*mid=b[i];
      right=b[i];*/
      //printf("left=%d mid=%d right=%d ans=%lld\n",left,mid,right,ans);
      ans+=min(b[n-3],b[n-2]);
    }else{
      ans+=b[n-2];
    }
  }
  printf("%lld",ans);
  return 0;

}