#include<iostream>
#include<vector>
#include<algorithm>

int main() {
	int n;
	std::cin >> n;

	std::vector<long long> v(n), dp(n);
	
	for (int i = 0; i < n; i++) {
		std::cin >> v[i];
	}

	dp[0] = v[0];

	for (int i = 1; i < n; i++) {
		dp[i] = std::max(dp[i - 1], v[i]);
		if (i > 1) dp[i] = std::max(dp[i], dp[i - 2] + v[i]);
	}

	std::cout << dp.back() << std::endl;
	return 0;
}