#include <bits/stdc++.h>
using namespace std;
#define REP(i,N) for(i=0;i<N;i++)
typedef long long ll;
typedef pair<int, int> P;
typedef struct{
  int first;
  int second;
  int third;
}T;

//昇順
bool comp_Se(T& l, T& r){
  return l.second < r.second;
}

int main(void){
  int N;
  cin >> N;
  int i;
  vector<int> v(N), dp(N+1,0);
  REP(i,N) cin >> v[i];
  dp[1] = v[0];
  for(i=1;i<N;i++){
    dp[i+1] = max(dp[i], dp[i-1]+v[i]);
  }
  cout << dp[N] << endl;
  return 0;
}