#include "bits/stdc++.h"
using namespace std;

int main() {
	int N;
	cin >> N;
	vector<int> V(N);
	for (int i = 0; i < N; i++)
	{
		cin >> V[i];
	}
	vector<int> dp(2);
	for (int i = 0; i < N; i++)
	{
		vector<int> dp2(2);
		dp2[0] = max(dp[0], dp[1]);
		dp2[1] = dp[0] + V[i];
		dp = dp2;
	}
	cout << max(dp[0], dp[1]) << endl;
}