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 Rust (1.15.1) (judge verdict: Accepted)

fn input_t<T: std::str::FromStr>() -> T {
	let mut s = String::new();
	std::io::stdin().read_line(&mut s).unwrap();
	s.trim().parse().ok().unwrap()
}

fn input_vt<T: std::str::FromStr>() -> Vec<T> {
	let mut s = String::new();
	std::io::stdin().read_line(&mut s).unwrap();
	s.trim().split_whitespace().map(|x| x.parse().ok().unwrap()).collect()
}

fn main() {
	let     n  = input_t::<usize>();
    let     xs = input_vt::<u32>();
    let mut c  = xs[0] + xs[n - 2];
    
    for i in 1..(n - 1) {
    	c += std::cmp::min(xs[i - 1], xs[i]);
    }
    
	println!("{}", c);
}