// I SELL YOU...! 
#include<iostream>
#include<vector>
#include<algorithm>
#include<functional>
#include<queue>
using namespace std;
typedef long long ll;
typedef pair<ll,ll> P;
signed main(){
  ll n;
  cin >> n;
  ll v[n],dp[n+1][2];
  fill(dp[0],dp[n+1],0);
  for(int i=0;i<n;i++){
    cin >> v[i];
  }
  for(int i=0;i<n;i++){
    dp[i+1][0]=max(dp[i][0],dp[i][1]);
    dp[i+1][1]=dp[i][0]+v[i];
  }
  cout << max(dp[n][0],dp[n][1])<<endl;
}