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 input1<T: std::str::FromStr> () -> Result<T, T::Err> {
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).unwrap();
    n.trim().parse()
}

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

fn min(a: usize, b: usize) -> usize {
    if a < b { a } else { b }
}

fn main() {
    let n: usize = input1().unwrap();
    let mut result = [100000; 100];
    for (i, b) in input_arr::<usize>().into_iter().enumerate() {
        result[i] = min(result[i], b);
        result[i + 1] = min(result[i + 1], b);
    }

    println!("{}", result.iter().take(n).sum::<usize>());
}