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

typedef pair<int,int> P;
typedef long long ll;

#define rep(i,n) for(int i=0;i<n;i++)
#define pb push_back
#define inf INT_MAX/4
#define ALL(v) v.begin(),v.end()

int main(void){

  int dp[1001];
  rep(i,1001) dp[i] = 0;
  int N;

  cin >> N;
  int cost[1001];
  for(int i = 1; i <= N; i++) cin >> cost[i];

  dp[0] = 0;
  dp[1] = cost[1];
  for(int i = 2; i <= N; i++){
    dp[i] = max(dp[i-1], dp[i-2]+cost[i]);
  }

  int res = -1;

  for(int i = 1; i <= N; i++) res = max(res, dp[i]);

  cout << res << endl;

  return 0;
}