#include<bits/stdc++.h>
using namespace std;
using Int = long long;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}

//INSERT ABOVE HERE
signed main(){
  Int n;
  cin>>n;
  vector<Int> v(n);
  for(Int i=0;i<n;i++) cin>>v[i];

  const Int INF = 1e8;
  vector<Int> dp1(n+1,-INF);
  vector<Int> dp2(n+1,-INF);
  dp1[0]=0;

  for(Int i=0;i<n;i++){
    chmax(dp1[i+1],dp1[i]);
    chmax(dp1[i+1],dp2[i]);
    chmax(dp2[i+1],dp1[i]+v[i]);
  }
  cout<<max(dp1[n],dp2[n])<<endl;
  return 0;
}