#include <iostream>
 
using namespace std;
 
void houseRobbery(int houseCount, unsigned long *maxSum, unsigned long *initialHouses) {
	/*
	A function that, through dynamic programming, calculates the maximum production of houses not standing nearby.
	The function does not return anything, since it modifies arrays through pointers
	*/
 
	// Initial state values for the first two houses
	maxSum[0] = initialHouses[0];
	maxSum[1] = max(initialHouses[0], initialHouses[1]);
 
	// Since by condition it is given that we cannot rob two houses in a row, 
	// then we will take the maximum house of two: maxSum[i - 1] and maxSum[i - 2] + initialHouses[house] 
	// (where initialHouses[house] is the amount of money in the i-th house)
	for (int house = 2; house < houseCount; house += 1) {
		maxSum[house] = max(maxSum[house - 1], maxSum[house - 2] + initialHouses[house]);
	}
}
 
int main() {
	int houseCount;
	cin >> houseCount;
 
	// Initialize the arrays not containing negative values
	unsigned long initialHouses[houseCount], maxSum[houseCount];
 
	// Filling the initial array of houses with user input
	for (int element = 0; element < houseCount; element += 1) {
		cin >> initialHouses[element];
	}
 
	// Calling the function
	houseRobbery(houseCount, maxSum, initialHouses);
 
	cout << maxSum[houseCount - 1];
	return 0;
}

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