#include <iostream>
#include <cstdio>
#include <cmath>
#include <vector>
#include <queue>

#include <map>
#include <set>
#include <string>
#include <algorithm>
#include <functional>
using namespace std;
#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#define INF 1<<30
#define ALEN(ARR) (sizeof(ARR) / sizeof((ARR)[0]))
#define MP make_pair
#define mp make_pair
#define pb push_back
#define PB push_back
#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define ll long long
#define ull unsigned long long
#define MOD 1000000007

int dp[1010];

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout.precision(16);

  int N;
  cin >> N;
  int V[N];
  REP(i, N) cin >> V[i];

  dp[0] = V[0];
  dp[1] = max(V[0], V[1]);
  FOR(i, 2, N) dp[i] = max(dp[i-1], dp[i-2]+V[i]);

  cout << dp[N-1] << endl;
  return 0;
}