#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

int main() {
	int n;
	cin >> n;
	vector<int> v(n);
	for (int i = 0; i < n; i++) {
		cin >> v[i];
	}

	static int dp[1010][2]; // i, takeprev
	for (int i = 0; i < 1010; i++) {
		for (int j = 0; j < 2; j++) {
			dp[i][j] = -1e9;
		}
	}

	dp[0][0] = 0;

	for (int i = 0; i < n; i++) {
		for (int j = 0; j < 2; j++) {
			if (!j) {
				dp[i + 1][1] = max(dp[i + 1][1], dp[i][j] + v[i]);
			}
			dp[i + 1][0] = max(dp[i + 1][0], dp[i][j]);
		}
	}

	int ans = max(dp[n][0], dp[n][1]);
	cout << ans << endl;

	return 0;
}