#include <bits/stdc++.h>
using namespace std;

int main() {
	int n;
	cin>>n;
	vector<int> arr(n+1,0);
	for(int i=1;i<=n;i++){
		int element;
		cin>>element;
		arr[i]=element;
	}
	vector<int> dp(n+1, 0);
	dp[1]=max(arr[1],0);      //empty subset can be an answer
	dp[2]=max(max(arr[1], arr[2]), 0);
	for(int i=3;i<=n;i++){
		dp[i]=max(dp[i-1], arr[i]+dp[i-2]);
	}
	cout<<dp[n];
	return 0;
}