#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int main() {
    int n;
    cin >> n;
    int a[n];
    for (int i=0;i<n;i++)cin>>a[i];
    ll dp[n+1];
    dp[0]=0;
    dp[1]=a[0];
    for (int i=2;i<=n;i++)
        dp[i]=max(dp[i-2]+a[i-1], dp[i-1]);
    cout << dp[n] << endl;
    return 0;
}