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 main() {
    let n: usize = {
        let mut line = String::new();
        std::io::stdin().read_line(&mut line);
        line.trim().parse().unwrap()
    };
    let b: Vec<i64> = {
        let mut line = String::new();
        std::io::stdin().read_line(&mut line);
        line.split_whitespace().map(|a| a.parse().unwrap()).collect()
    };
    let mut a: Vec<i64> = vec![1 << 40; n];
    for i in 0..(n-1) {
        a[i] = std::cmp::min(a[i], b[i]);
        a[i + 1] = std::cmp::min(a[i + 1], b[i]);
    }
    println!("{}", a.iter().fold(0i64, |sum, &a| sum + a));
}