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 (1.42.0) (judge verdict: Accepted)

use std::io;

fn main() {
    //数列Aの個数
    let mut n = String::new();

    io::stdin()
        .read_line(&mut n)
        .expect("Failed to read line");

    let n: i32 = n.trim().parse().expect("Please type a number!");

    let mut sum_c : i32 = 0;
    let mut line = String::new();

    let mut cnt = 1;

    io::stdin()
        .read_line(&mut line).unwrap();
        line.trim_end().to_owned(); // 改行コードが末尾にくっついてくるので削る

        let mut ws = line.split_whitespace(); // 空白区切りの単語に分解する
    let mut b0: i32 = ws.next().unwrap().parse().unwrap(); // イテレータから値を取り出して整数に

    sum_c += b0;
    if n <= 2 {
        println!("{}", sum_c * 2);
        return;
    }

    while cnt < n - 1 {
        //let mut b1 = String::new();

        let b1: i32 = ws.next().unwrap().parse().unwrap(); // イテレータから値を取り出して整数に

        sum_c += min(b0, b1);
        b0 = b1;
        cnt += 1;

    }
                    sum_c += b0;

                    println!("{}", sum_c);
    }

    ///小さい方の値を返す
    fn min(x: i32, y: i32) -> i32{
        if x < y{
            return x;
        }
        return y;
    }