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 <math.h>
#include <limits.h>
#include <stdlib.h>
long long N,W;

int 
main(){
	long long X,K;
	long long B[110];

	scanf("%lld",&N);
	long long i,j;

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


	long long sum=0;
	int prev_a =0;
	for(i=0;i<N;i++){
		if(i==0)sum +=B[0]; // B[i]
		else if(i==N-1) {
			sum += B[i-1];
			//printf("%d'%lld\n",i,B[i-1]);
		}
		else if(i>=1){
			if( B[i-1]<B[i]){
				sum+= B[i-1];
				//printf("+%lld\n",B[i-1]);
			}
			else {
				sum += B[i];
				//printf("++%lld\n",B[i]);
			}
		}
	}
	printf("%lld\n",sum);
 return 0;
}