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 Python (3.8.2) (judge verdict: Accepted)

#入力:[n1,n2,...nk](int:整数配列)
def input_array():
	return list(map(int,input().split()))

n=int(input())
B=input_array()
A=[B[0]]
ans=B[0]

for i in range(1,n):
	if A[i-1] > B[i-1]:
		ans=ans-A[i-1]+B[i-1]
		A[i-1]=B[i-1]
	ans+=B[i-1]
	A.append(B[i-1])

print(ans)