#include <iostream>
#include <vector>

int main()
{
	int n;
	std::cin >> n;
	std::vector<int> v(n);
	for (int i = 0; i < n; ++i) {
		std::cin >> v[i];
	}
	
	std::vector<int> dp(n + 1);
	dp[0] = 0;
	dp[1] = v[0];
	
	for (int i = 2; i <= n; ++i) {
		dp[i] = std::max(dp[i - 1], dp[i - 2] + v[i - 1]);
	}
	
	std::cout << dp[n] << std::endl;
	
	return 0;
}