House Robber

Given an array of non-negative integers representing money stashed in houses along a street, find the maximum amount you can rob without robbing two adjacent houses (doing so trips the alarm).

Example

Input: 1 2 3 1 Output: 4 (rob house 1 and house 3: 1 + 3 = 4)

Approach

At each house, you either skip it (carry forward the best total so far) or rob it (best total from two houses back, plus this house's value). Track just the previous two running totals instead of a full array — O(n) time, O(1) space.

Input format

Line 1: the array, space-separated

Print the maximum amount.