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

signed main(){
  cin.tie(0);
  ios::sync_with_stdio(false);

  int n; cin >> n;
  vector<int> v(n);
  for(int i = 0; i < n; i++){
    cin >> v[i];
  }
  if(n < 2){
    cout << v[0] << endl;
    return 0;
  }

  vector<int> dp(n);
  dp[0] = v[0];
  dp[1] = v[1];
  if(n > 2) dp[2] = v[0] + v[2];
  for(int i = 3; i < n; i++){
    dp[i] = max(dp[i-2],dp[i-3]) + v[i];
  }
  cout << max(dp[n-1],dp[n-2]) << endl;

  return 0;
}