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

int main()
{
	int N; vector<int> V; vector<pair<int, bool>> memo;
	cin >> N;
	V.resize(N + 1);
	V[0] = 0;	//memoと合わせる
	for (int i = 1; i <= N; ++i)
		cin >> V[i];

	memo.resize(N + 1);
	memo[0] = pair<int, bool>(0, true);
	memo[1] = pair<int, bool>(V[1], true);
	for (int p = 2; p <= N; ++p)
	{
		int i; bool b;
		if (memo[p - 1].second == true)
		{
			if (memo[p - 1].first < memo[p - 2].first + V[p])
			{
				i = memo[p - 2].first + V[p];
				b = true;
			}
			else
			{
				i = memo[p - 1].first;
				b = false;
			}
		}
		else
		{
			i = memo[p - 1].first + V[p];
			b = true;
		}
		memo[p] = pair<int, bool>(i, b);
	}

	cout << memo[N].first << endl;


	return 0;
}