#include<bits/stdc++.h>
using namespace std;
#define T 10

int main(){
  int N, v[10100] = {}, V;

  cin>>N;

  for(int i = 1+T; i <= N+T; i++){
    cin>>V;
    v[i] = max(V + v[i-2], v[i-1]);
  }

  cout<<v[N+T]<<endl;

  return 0;
}