#include <iostream>
#include <cstdio>
#include <vector>
#include <list>
#include <map>
#include <queue>
#include <algorithm>
#define rep(i, n) for(int (i)=0; (i)<(n); ++(i))
using namespace std;

int main()
{
    int n;
    cin >> n;
    vector<int> val = vector<int>(n);
    vector<int> ans = vector<int>(n);
    rep(i,n) {
        int x;
        cin >> x;
        val[i] = x;
        ans[i] = 0;
    }
    ans[0] = val[0];
    ans[1] = max(val[0], val[1]);

    for(int i=3; i<n; ++i) {
        ans[i] = max(ans[i-2] + val[i], ans[i-1]);
    }

    cout << ans[n-1] << endl;
	return 0;
}