#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <numeric>
#include <stack>
#include <utility>
#include <queue>
//#include <random>
#include <time.h>

#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)

#define SWAP(a,b) (a ^= b,b = a ^ b,a ^= b)
#define swap(type,a,b) do{type _c;_c=a;a=b;b=_c;}while(0)

using namespace std;
typedef long long int lint;

template <typename _Ty>
ostream& operator << (ostream& ostr, const vector<_Ty>& v) {
	if (v.empty()) {
		cout << "{ }";
		return ostr;
	}
	cout << "{" << v.front();
	for (auto itr = ++v.begin(); itr != v.end(); itr++) {
		cout << ", " << *itr;
	}
	cout << "}";
	return ostr;
}

int yuki0045()
{
	int n, tmp;

	cin >> n;

	int* v = new int[n + 3];
	v[0] = v[1] = v[2] = 0;
	for (int i = 0; i < n; i++) {
		cin >> tmp;
		v[i + 3] = max(v[i], v[i + 1]) + tmp;
	}

	cout << v[n + 2] << endl;
	
	delete[] v;

	return 0;
}


int main()
{
	//clock_t start, end;
	//start = clock();

	yuki0045();

	//end = clock();
	//printf("%d msec.\n", end - start);

	return 0;
}