#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i = (a); i < (b); ++i)
#define REP(i,n) FOR(i,0,n)
#define SZ(n) (int)(n).size()
#define ALL(n) (n).begin(), (n).end()
#define MOD 1000003
#define INF 100000000
using namespace std;
typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PI;


int main() {
	int n;
	cin >> n;
	int v[1010] = {};
	REP(i, n) cin >> v[i];
	int s[1010] = {};
	REP(i, n) s[i + 1] = v[i];
	FOR(i, 3, n + 1) {
		if (s[i - 2] >= s[i - 3]) s[i] += s[i - 2];
		else s[i] += s[i - 3];
	}
	cout << s[n] << endl;
	return 0;
}