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>
#include <stdlib.h>

int main(){
  int N,i=0,sum=0;
  scanf("%d",&N);
  int A[N],B[N-1];
  while(i!=N-1){
    scanf("%d",&B[i++]);
  }
  for(i=0;i<N;i++) A[i]=0;
  i=1;
  
  A[0]=B[0]; A[N-1]=B[N-2];
  if(i<N-2){
    while(i!=N-1){
      A[i]=B[i-1];
      if(A[i]>B[i]) A[i]=B[i];
      i++;
    }
  }
  for(i=0;i<N;i++) sum+=A[i];
  printf("%d\n",sum);
  return 0;
}