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 (2.4.0) (judge verdict: Accepted)

from __future__ import print_function
# import numpy as np
# import numpypy as np
import sys
input = sys.stdin.readline

def eprint(*args, **kwargs):
    print(*args, file=sys.stderr, **kwargs)
    return

import math
import string
import fractions
from fractions import Fraction
from fractions import gcd

def lcm(n,m):
    return int(n*m/gcd(n,m))

import re
import array
import copy
import functools
import operator

import collections
import itertools
import bisect
import heapq


from heapq import heappush
from heapq import heappop
from heapq import heappushpop
from heapq import heapify
from heapq import heapreplace

from queue import PriorityQueue as pq

def reduce(p, q):
    common = fractions.gcd(p, q)
    return (p//common , q//common )
# from itertools import accumulate
# from collections import deque

import random


def main():
    n=int(input())
    b = list(map(int, input().split()))
    
    sum=0
    sum+=b[0]
    sum+=b[n-2]
    for i in range(n-2):
        sum+=min(b[i],b[i+1])
    print(sum)
    return

if __name__ == '__main__':
    main()