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: Wrong Answer)

#include <stdio.h>

int max(int a, int b){
    if(a > b)
        return a;
    else  
        return b;
}
int min(int a, int b){
    if(a < b)
        return a;
    else  
        return b;
}


int main(void){
    //input
    int N;  scanf("%d",&N);
    int A[N];
    int B[N-1];     
    for(int i = 0 ;i < N-1; i++){
        scanf("%d",&B[i]);
        }

    //cal
    int sum = 0;
    A[N-1]=B[N-2]; A[0]=B[0];
    if(N>4){
        for(int i = N-1; i>1; i--){
            A[i] = min(B[i], B[i-1]);
        }
        for(int i = 0; i < N; i++){
            sum += A[i];
        }
    }else if(N==2){
        sum = B[0]*2;
    }else{
        A[1] = min(B[0],B[1]);
        //A[2] = B[1];
        //printf("%d %d %d %d\n",A[0],A[1],A[2],A[3]);
        sum = A[0]+A[1]+A[2];
    }


    // for(int i = 0; i < N; i++){
    //     printf("%d番目のAは%d\n",i+1,A[i]);
    // }
    //output
    printf("%d\n",sum);
}