#include <bits/stdc++.h>

using namespace std;

int main() {
	int n;
	cin >> n;
	vector<int> v(n);
	int dp[1000][2];
	for (int i = 0;i < n;i++) {
		cin >> v[i];
	}
	if (n == 1) {
		cout << v[0] << endl;
		return 0;
	}
	dp[0][0] = 0;
	dp[0][1] = v[0];
	dp[1][0] = v[0];
	dp[1][1] = v[1];
	for (int i = 2;i < n;i++) {
		dp[i][0] = max(dp[i - 2][1], dp[i - 1][1]);
		dp[i][1] = max(dp[i - 2][1], dp[i - 1][0]) + v[i];
	}

	cout << max(dp[n-1][0],dp[n-1][1]) << endl;

	return 0;
}