#include <bits/stdc++.h>
using namespace std;
int N;
int V[1000];
int dp[1000];

int recursive(int pos) {
	if(pos >= N) return 0;
	if(dp[pos] >= 0) return dp[pos];
	dp[pos] = max(recursive(pos + 2) + V[pos], recursive(pos + 1));
	return dp[pos];
}

int main() {
	cin >> N;
	for(int i = 0; i < N; i++) {
		cin >> V[i];
		dp[i] = -1;
	}
	cout << recursive(0) << endl;
	return 0;
}