#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <string>
#include <bitset>
#include <cstdio>
#include <limits>
#include <vector>
#include <climits>
#include <cstring>
#include <cstdlib>
#include <fstream>
#include <numeric>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <iomanip>
#include <cctype>
using namespace std;
typedef long long ll;

int main()
{
	int n, a, dp[101] = {};
	vector<int>v;
	cin >> n;
	v.push_back(0);
	for (int i = 1; i <= n; i++)
	{
		cin >> a;
		v.push_back(a);
	}
	dp[1] = v[1];
	for (int i = 2; i <= n; i++)
	{
		dp[i] = max(dp[i - 1], dp[i - 2] + v[i]);
	}
	cout << dp[n] << endl;
	return 0;
}