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

int deli[1000];
int memo[1000];
int N;

int solve(int n) {
  if (n > N) return 0;
  if (memo[n] != -1) return memo[n];
  return memo[n] = max(solve(n+1), solve(n+2) + deli[n]);
}

int main(void) {
  cin >> N;
  for (int i = 0; i < N; i++) {
    memo[i] = -1;
    cin >> deli[i];
  }
  cout << solve(0) << endl;
  return 0;
}