#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <complex>
#include <queue>
#include <set>
#include <map>

using namespace std;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)

typedef long long ll;

int main() {

  int N; cin >> N;
  int v[N];
  rep(i, N) {
    cin >> v[i];
  }

  ll dp[N+1]; fill(dp, dp+N+1, 0);
  dp[0] = 0, dp[1] = v[0];

  REP(i, 2, N+1) {
    dp[i] = max(dp[i-1], dp[i-2]+v[i-1]);
  }
  cout << dp[N] << endl;

  return 0;
}