#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const double PI = acos(-1);
const ll MOD = 1000000007;

int main() {
  int N; cin >> N;
  vector<int> V(N);
  for (int i = 0; i < N; i++) cin >> V[i];
  vector<int> ans(N);
  
  for (int i = 0; i < N; i++) {
    if (i == 0) ans[i] = V[i];
    else if (i == 1) ans[i] = max(V[i],V[i-1]);
    else ans[i] = max(ans[i-1],ans[i-2]+V[i]);
  }
  
  cout << ans[N-1] << endl;
}