#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main() {
    int n;
    cin >> n;
    vector<int> a(n);
    
    for (int i = 0; i < n; ++i) {
        cin >> a[i];
    }
    
    if (n == 0) {
        cout << 0 << endl;
        return 0;
    }
    
    if (n == 1) {
        cout << max(0, a[0]) << endl;
        return 0;
    }
    
    vector<int> dp(n);
    dp[0] = max(0, a[0]);
    dp[1] = max(dp[0], a[1]);
    
    for (int i = 2; i < n; ++i) {
        dp[i] = max(dp[i-1], a[i] + dp[i-2]);
    }
    //for god's sike work
    cout << dp[n-1] << endl;
    
    return 0;
}