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

int main(){
  int n,flag;
  flag=0;
  vector<int > v;
  int a[1000]={0};
  cin>>n;
  for(int i=0;i<n;i++){
    int tmp;
    cin>>tmp;
    v.push_back(tmp);
  }
  if(n>2){
    a[1]=v.at(0);
    a[2]=max(v.at(0),v.at(1));
    for(int i=3;i<n;i++){
      if(a[i-1]<a[i-2]+v.at(i)&&flag==0){
        a[i]=a[i-2]+v.at(i);
        flag=1;
      }else{
        a[i]=a[i-1];
        flag=0;
      }
    }
    cout<<a[n-1]<<endl;
  }else{
    cout<<v.at(0)<<endl;
  } 
}