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 MIN(A,B) ((A)<(B)?(A):(B))

int B[1000];

#define Inf 100000

int main(){
  int n, a, i;
  scanf("%d", &n);
  B[n]=Inf;
  for (i=1; i<=n-1; i++){
    scanf("%d", &B[i]);
  }
  B[0]=B[1];
  a=0;
  for (i=1; i<=n; i++){
    a+=MIN(B[i], B[i-1]);
  }
  printf("%d\n", a);

}