#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

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