#include <bits/stdc++.h>

using namespace std;

int N;
int C[1000];
int memo[1000];

int dfs(int i)
{
    if (i >= N) return 0;

    if (memo[i] >= 0) return memo[i];

    return memo[i] = C[i] + max(dfs(i+2), dfs(i+3));
}

int main()
{
    memset(memo, -1, sizeof(memo));
    cin >> N;
    for (int i = 0; i < N; ++i) cin >> C[i];
    cout << max(dfs(0), dfs(1)) << endl;
}