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 main(){
	int n,flag;
	scanf("%d",&n);
	int b[n-1],max=0;
	for(int i=0;i<n-1;i++){
		scanf("%d",&b[i]);
		//printf("%d\n",b[i]);
	}
	int index=0;
	int count=0;
	while((n-1)>index){
		while(1){
			count++;
			if(count>=n-1)break;
			if(b[count]>b[count-1])break;
			flag=1;
		}
	//	printf("b[%d]:%d\n",count-1,b[count-1]);
		if(flag){
			for(int i=index;i<count;i++){
				b[i]=b[count-1];
			}
		}
		index=count;
	}
	for(int i=0;i<n-1;i++){
		max+=b[i];
		//("%d\n",b[i]);
	}
	printf("%d\n",b[0]+max);
	return 0;
}