#include <cstdio>
#include <iostream>
#include <algorithm>
using namespace std;


int main()
{
    int N, V[1000], dp[1000];

    cin >> N;
    for (int i=0; i<N; i++) cin >> V[i];

    dp[0] = V[0]; dp[1] = max(V[0], V[1]);
    for (int i=2; i<N; i++) dp[i] = max(dp[i-2] + V[i], dp[i-1]);

    cout << dp[N-1] << endl;
}