#include <iostream>
#include <algorithm>
using namespace std;
#define REP(i, N) for(int i=0;i<(N);++i)

int main() {
    int n; cin >> n;
    int v[1000] = {}; REP(i, n) cin >> v[i];
    int d[1000] = {};
    d[0] = v[0];
    d[1] = max(d[0], v[1]);

    for (int i = 2; i < n; ++i) {
        d[i] = max(d[i-1], d[i-2] + v[i]);
    }
    cout << d[n-1] << endl;
}