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 C (GCC 5.4.1) (judge verdict: Accepted)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

#define input_i(x) scanf("%d", &x)
#define input_lli(x) scanf("%lld", &x)
#define input_s(x) scanf("%s", x)

#define BUFSIZE 1001

int main(int argc, char const *argv[]) {
    int N, i;
    input_i(N);
    int B[N];
    for(i= 0; i < N - 1; i++) {
        input_i(B[i]);
    }
    B[N - 1]= B[N - 2];
    int ans= 0;
    ans+= B[0];
    for(i= 1; i < N - 1; i++) {
        int min= (B[i] < B[i - 1]) ? B[i] : B[i - 1];
        ans+= min;
    }
    ans+= B[N - 1];

    printf("%d\n", ans);

    return 0;
}