#include <iostream>
#include <string>
#include <vector>

using namespace std;

#define INF 		2000000007

#define REP(i,n)	for(int i=0;i<n;++i)

int main(){
	int N;
	cin >> N ;

	vector<int> K(N);
	for(int i=0;i<N;++i)
		cin >> K[i];

	vector<int> DP(N+10,0);

	int base = 3;

	for(int i=base;i<N+base;++i){	// 寿司番号
		//cout << DP[i-2]+K[i-base] << " " << DP[i-3]+K[i-base] << endl;
		DP[i] = max(DP[i],DP[i-2]+K[i-base]);
		DP[i] = max(DP[i],DP[i-3]+K[i-base]);
	}
	/*for(auto t:DP)
		cout << t << " " ;
	cout << endl;//*/

	cout << DP[N+base-1] << endl;

	return 0;
}