#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
using namespace std;

#define ll long long
#define INF (1 << 30)
#define INFLL (1LL << 60)

int sushi[1010] = {};
int n;
int memo[1010];

int dp(int now){
	if(now >= n) return 0;
	if(memo[now] != INF) return memo[now];

	int a,b;
	a = dp(now + 1);
	b = dp(now + 2) + sushi[now];

	return memo[now] = max(a,b);
}

int main() {
	for(int i = 0;i < 1010;i++){
		memo[i] = INF;
	}
	cin >> n;
	for(int i = 0;i < n;i++){
		cin >> sushi[i];
	}

	cout << dp(0) << endl;
	return 0;
}