#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;
}