#include <bits/stdc++.h>

using namespace std;


ifstream fin("oo.in");
ofstream fout("oo.out");
/**

max(dp[i-1]
*/

int dp[200005], a[200005], n, dp2[100004];

int main()
{
    fin >> n ;
    for(int i = 1; i <= n; i++)
        fin >> a[i];
    dp[1] = a[1] + a[2];
    dp[2] = dp[1];
    for(int i = 3; i < n; i++)
        dp[i] = max(dp[i-1], dp[i-3] + a[i - 1] + a[i]);
    dp2[1] = 0;
    dp2[2] = a[2] + a[3];
    for(int i = 3; i <= n; i++)
        dp2[i] = max(dp2[i-1], dp2[i-3] + a[i - 1] + a[i]);
    fout << max(dp[n], dp2[n]);
    return 0;
}