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 LuaJIT (2.0.4) (judge verdict: Wrong Answer)

local function reada(n,m)m=m or 1 r={}for i=1,m do r[i]={}end for i=1,n do for j=1,m do r[j][i]=io.read"*n"end end return unpack(r)end
N=io.read"*n"
B=reada(N-1)
s=0
b=B[N-1]
for i=N-1,1,-1 do
	b=math.min(b,B[i])
	s=s+b
end
print(s+B[1])