#include<bits/stdc++.h>
using namespace std;

#define endl '\n'
#define ALL(g) (g).begin(),(g).end()
#define REP(i, x, n) for(int i = x; i < n; i++)
#define rep(i,n) REP(i,0,n)
#define F(i,j,k) fill(i[0],i[0]+j*j,k)
#define P(p) cout<<(p)<<endl;
#define SORT(v) sort(all(v))
#define SORTD(v) sort(all(v), greater<int>())
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define INF 1<<30
#define v(T) vector<T>
#define vv(T) v(v(T))
#define print(x) cout<<x<<endl
#define printv(v) for(auto i : v){cout<<i<<" ";}cout<<endl
#define printu(v) for(auto i : v){print(i);}
#define readv(v, n) for (int i=0;i<n;i++)cin >> v[i]
typedef vector<int> vi;
typedef vector<long long> vl;
typedef vector<double> vd;
typedef pair<int,int> pii;
typedef pair<long,long> pll;
typedef long long ll;

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

int i, j, k;
int dp[1004];
int main()
{
	cin.tie(0);
	ios::sync_with_stdio(false);
	int n;
	cin >> n;
	rep(i, n) {
		int k;
		cin >> k;
		dp[i + 3] = k;
	}
	REP(i, 3, n + 3) {
		dp[i] = std::max({dp[i] + dp[i - 2], dp[i - 1], dp[i - 3]});
	}
	print(dp[n + 2]);
	return 0;
}