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)

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

//scanf("%d",&x);
//printf("%d",x);
//for(i=0;i<N;i++){  }
//if( == ){  }else{  }
//while( ){  }

/*
int N, i;
int H[100];
scanf("%d", &N);
for (i = 0; i < N; i++) scanf("%s", &H[i]);
*/

int main()
{
	int N, i,S=0;
	int A[99];
	int B[99];
	scanf("%d", &N);
	for (i = 0; i < N-1; i++) scanf("%d", &B[i]);

	if (N >= 3) {

		A[0] = B[0];
		A[1] = B[0];

		for (i = 2; i < N - 1; i++) {
			if (B[i - 1] > B[i]) {
				A[i] = B[i];
			}
			else A[i] = B[i - 1];
		}

		A[N - 1] = B[N - 2];

		for (i = 0; i < N; i++) {
			S += A[i];
		}

		printf("%d", S);

	}
	else {
		int t = 2 * B[0];
		printf("%d", t);
	}

	
}