#include<iostream>
#include<algorithm>
using namespace std;
int dp[1001];
int main(){
	int n; cin >> n;
	for (int i = 1; i <= n; i++) cin >> dp[i];
	for (int i = 2; i <= n; i++){
		dp[i] = max(dp[i - 1], dp[i] + dp[i - 2]);
	}
	cout << dp[n] << endl;
	return 0;
}