101402: [AtCoder]ABC140 C - Maximal Value
Memory Limit:256 MB
Time Limit:2 S
Judge Style:Text Compare
Creator:
Submit:0
Solved:0
Description
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