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>
#include <stdlib.h>
#include <math.h>


int main(void) {
int N;
scanf("%d",&N);
int arr[N];
int res[N+1];
memset(arr,0,N*sizeof(*arr));
memset(res,0,(N+1)*sizeof(*res));

for (int i=1;i<=N-1;i++)
scanf("%d",&arr[i]);
for (int i=1;i<=N;i++)
res[i]=arr[i];
res[N]=arr[N-1];

for (int i=1;i<=N-1;i++)
if (arr[i]<arr[i+1]) res[i+1]=arr[i];

res[N]=arr[N-1];

int sum =0;

for (int i=1;i<=N;i++)
sum+=res[i];

printf("%d",sum);
return EXIT_SUCCESS;
}