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

//これも動的計画法で行けそう？
const int INF = 99999999;
vector<int> sushi;
//vector<int> umai(100001, INF);

int dp(int index){
	if(index < 0) return 0;
	return max(dp(index-1), dp(index-2) + sushi[index]);
}
	

int main(){
	int n, tmp;
	cin >> n;
	for(int i=0; i<n; i++){
		cin >> tmp;
		sushi.push_back(tmp);
	}


	cout << dp(n) << endl;
		
		/*
	umai[0] = -100;
	for(int i=0; i<n; i++){
		for(int j=100000; j >=0 ; j--){
			if(umai[j] != INF){
				if(umai[j] != i-1) umai[j+sushi[i]] = i;
			}
		}
	}


	//for(int i=1; i<20 ; i++) cout << umai[i] <<endl;
	for(int i=100000; i>=0; i--) {
		if(umai[i] != INF){
			cout << i << endl;
			return 0;
		}
	}*/
}