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)

import sys
import math

def input():
    return sys.stdin.readline().strip()

def iinput():
    return int(input())

def finput():
    return float(input())

def tinput():
    return input().split()

def rinput():
    return map(int, tinput())

def rlinput():
    return list(rinput())

def pro(k, l, n):
    if l < n:
        if k == 0:
            return(n - l)
        return (n - l + 2)
    if l == n:
        if k == 0:
            return 0
        elif k == 1:
            return 1
        return 3
    else:
        l -= n - 1
        if l == k:
            return 1
        elif l > k:
            return 0
        if l < k - 1:
            return 2
        else:
            return 3
            

def rt(k, l , n):
    if k < n:
        if l == 0:
            return (k * 2 + n)
        return (n + k * 2 - 1)
    elif k == n:
        if l == 1:
            return (k * 3 - 2)
        elif l == 0:
            return (k * 3)
        return (k * 3 - 3)
    else:
        k -= n - 1
        if k == l:
            return (n * 3 - 2)
        elif k > l:
            return (n * 3)
        if k < l - 1:
            return ((n - 1) * 3 - 1)
        else:
            return ((n - 1) * 3)



def main():
    n = iinput()
    a = rlinput()
    res = a[0] + a[-1]
    for i in range(n - 2):
        if a[i] > a[i + 1]:
            res += a[i + 1]
        else:
            res += a[i]
    print(res)
    
    
    
    
    


main()