#include <algorithm>
#include <iostream>
#include <cstdio>
#include <map>
#include <numeric>
#include <cmath>
#include <set>
#include <sstream>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <complex>
#include <string.h>
#include <unordered_set>
#include <unordered_map>
#include <tuple>
#include <iomanip>
using namespace std;

#define endl '\n'
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define uniq(v) (v).erase(unique((v).begin(), (v).end()), (v).end())

typedef long long ll;
typedef pair<int, int> P;
typedef unsigned int uint;
typedef unsigned long long ull;
struct pairhash {
public:
    template<typename T, typename U>
    size_t operator()(const pair<T, U> &x) const {
	size_t seed = hash<T>()(x.first);
	return hash<U>()(x.second) + 0x9e3779b9 + (seed<<6) + (seed>>2);
    }
};

const int inf = 1000000009;
const double eps = 1e-8;
int memo[1010];
int vs[1010];

int search(int k, int n) {
    if (k >= n) return 0;
    if (memo[k] < 0) {
	if (k >= n - 2) {
	    memo[k] = vs[k];
	} else {
	    memo[k] = vs[k] + max(search(k+2, n), search(k+3, n));
	}
    }
    return memo[k];
}

int solve(int n) {
    memset(memo, -1, sizeof(memo));
    for (int i = 0; i < n; i++)
	scanf("%d", &vs[i]);
    return max(search(0, n), search(1, n));
}

int main() {
    /*
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(15);
    */
    
    int n;
    scanf("%d", &n);
    printf("%d\n", solve(n));
}