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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
typedef long long ll;
long long MOD = 1e9 + 7;
using namespace std;

int main() {
  int N;
  cin >> N;

  int B[N];
  rep(i, N - 1) { cin >> B[i]; }

  ll result = 0;
  int tmp = 0;

  rep(i, N - 1) {
    if (i == 0) {
      result += B[0] + min(B[0], B[1]);
    } else if (i == N - 2) {
      if (i > 1) {
        result += min(B[i - 1], B[i]);
      }
      result += B[i];
    } else {
      result += min(B[i - 1], B[i]);
    }
  }

  cout << result << endl;
  return 0;
}