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

int dp[1005];//dp[i]はi番目までの皿を食べたときの最大値

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