You’re climbing a staircase with n stairs. On each step, you can either climb 2 stairs or climb only 1. As you step on each stair, you pay a cost associated with that stair. Your task is to climb to the very top by paying as little as possible.
Input
The first line of the input contains a single integer n (1 ≤ n ≤ 1000).
The next line contains the costs associated with each stair (0 ≤ ≤ 1000).
Output
The program should print the minimum cost to reach the top of the staircase.
Examples
Input
Output
3
10 12 25
12
10
1 20 1 1 1 20 1 2 20 1
7
Explanation
We stand in front of the staircase ⇒ the current cost is 0. We step on the second staircase ⇒ the cost is 12. Then we get out of the staircase by doing a step of length 2 ⇒ cost remains 12.