#include <iostream>
#include <algorithm>
using namespace std;
int main() {
    int n;
    cin >> n;
    if (n == 0) {
        cout << 0 << endl;
        return 0;
    }
    int a[n];
    for (int i = 0; i < n; ++i) {
        cin >> a[i];
    }
    int prev1 = 0;
    int prev2 = 0;
    for (int i = 0; i < n; ++i) {
        int current = max(prev1, prev2 + a[i]);
        prev2 = prev1;
        prev1 = current;
    }
    cout << prev1 << endl;    //t5bich babe 
    return 0;
}