#include<bits/stdc++.h>
using namespace std;
#define inf 1000000000
#define INF 1000000000000000
#define ll long long
#define ull unsigned long long
#define M (int)(1e9+7)
#define P pair<int,int>
#define PLL pair<ll,ll>
#define FOR(i,m,n) for(int i=(int)m;i<(int)n;i++)
#define RFOR(i,m,n) for(int i=(int)m;i>=(int)n;i--)
#define rep(i,n) FOR(i,0,n)
#define rrep(i,n) RFOR(i,n,0)
#define all(a) a.begin(),a.end()
#define IN(a,n) rep(i,n){ cin>>a[i]; }
const int vx[4] = {0,1,0,-1};
const int vy[4] = {1,0,-1,0};
#define PI 3.14159265
#define F first
#define S second
#define PB push_back
#define EB emplace_back
#define int ll
void init(){
  cin.tie(0);
  ios::sync_with_stdio(false);
}


main(){
  int n;
  cin>>n;
  vector<int> v(n);
  rep(i,n){
    cin>>v[i];
  }

  vector<int> dp(n,0);

  rep(i,n){
    if(i==0){
      dp[i]=v[i];
    }else if(i==1){
      dp[i]=max(dp[i-1],v[i]);
    }else{
      dp[i]=max(v[i]+dp[i-2],dp[i-1]);
    }
  }

  cout<<dp[n-1]<<endl;
}