#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using ull = unsigned long long;

#ifndef __MACRO_H__
#define __MACRO_H__

#define all(collection)  (collection).begin(), (collection).end()		// begin to end
#define rep(i, begin, end) for (ll i = begin; i < end; i++)				// repeat
#define repr(i, begin, end) for (ll i = begin; end < i; i--)			// repeat reverse

#endif

int main(void)
{
	ll n; cin >> n;

	// 最大で3つ前から取ってくるので、空要素を3つ追加
	n += 3;
	vector<ll> v(n);
	rep(i, 3, n)
		cin >> v[i];

	vector<ll> dp(n);
	rep(i, 3, n)
		dp[i] = max(dp[i-3] + v[i], dp[i-2] + v[i]);

	cout << max(dp[n-1], dp[n-2]);
	return 0;
}