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 PyPy3 (7.3.0) (judge verdict: Accepted)

import heapq
t = 1
def max(a,b):
	if a > b:
		return a
	return b
while t > 0:
	t -= 1
	# n = map(int,input().split())
	n = int(input())
	# a = list(map(int,input().strip().split()))[0:n]
	# b = list(map(int,input().strip().split()))[0:n]
	c = list(map(int,input().strip().split()))[0:n-1]
	b = []
	for i in range(n):
		b.append(0)
	b[0] = c[0]
	b[n-1] = c[n-2]
	for i in range(1,n-1):
		b[i] = min(c[i],c[i-1])
	ans = 0
	for i in range(n):
		ans += b[i]
	print(ans)
	# print(n*n*n)
	# m = 1000
	# i = 0
	# while i < n:
	# 	j = i
	# 	while j+1 < n and v[j+1] >= v[j]:
	# 		j += 1
	# 	x = m//v[i]
	# 	m = m%v[i]
	# 	temp = x*v[j]
	# 	m += temp
	# 	i = j+1
	# print(m)