## Goal

Rob is a robber. He wants to operate a last time in the neighborhood before he leaves.

He has been informed about the values of the content of each house of a street but he is careful and when he robs in a house he avoids the 2 houses aside (left and right).

What is the maximum money he can make without being caught?

! Be warned ! Some houses have been trapped. They have been rated with negative values.

For example, for a street of 3 houses with values: (A: 1) - (B: 2) - (C: 3), Rob shall visit houses A and C (he takes 4).

In this other street: (A: 1) - (B: 15) - (C: 10) - (D: 13) - (E: 16), Rob should avoid C and D and visit only B and E (he takes 31).
Input

**Line 1:** An integer `N` for the number of houses in the street.

**Next **`N` lines: The value `housevalue` of the nth house content.

Output

**Line 1:** A single integer being the maximum amount Rob can make in the street.

Constraints

1 ≤ `N` ≤ 100

`housevalue` < 10^13