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

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int N; cin >> N;
    int a = 0,b = 0;
    while(N--){
        int v; cin >> v;
        int c = max(a+v,b);
        a = b,b = c;
    }
    cout << b << "\n";
}