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>
#define SIZE10 100000

typedef long long int ll;
typedef unsigned char u8;

int main(void){
    int N;
    int B[256];
    int sum;
    int i = 0;

    scanf("%d", &N);
    for(i = 0; i < N-1; i++){
        scanf("%d", &B[i]);
    }
    sum = B[0];

    for(i = 1; i < N; i++){
        if(B[i] == B[i-1]){
            sum += B[i];
            sum += B[i+1];
            i++;
        }else if(B[i] > B[i-1] && B[i+1] >= B[i] && i != N-2){
            sum += B[i-1];
            sum += B[i];
            i++;
        }else if(B[i] > B[i-1] && B[i] > B[i+1] && i != N-2){
            sum+=B[i-1];
        }else if(B[i] < B[i-1] && B[i] > B[i+1] && i != N-2){
            sum += B[i];
        }else if(B[i] < B[i-1] && B[i] <= B[i+1] && i != N-2){
            sum += B[i]*2;
            i++; 
        }else if(i == N-1 || i == N-2){
            sum += B[i-1];
        }
    }

    printf("%d", sum);
    return 0;
}