#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;
    int val[1001];
    int ans[1001][2];
    rep(i,n) {
        cin >> val[i];
    }
    ans[0][0] = 0;
    ans[0][1] = val[0];
    ans[1][0] = val[0];
    ans[1][1] = val[1];

    for(int i=2; i<n; ++i) {
        ans[i][0] = max(ans[i-1][1], ans[i-2][1]);
        ans[i][1] = max(ans[i-1][0], ans[i-2][0]) + val[i];
    }

    cout << max(ans[n-1][0], ans[n-1][1]) << endl;
	return 0;
}