#include<bits/stdc++.h>
using namespace std;
int n;
int v[1000];
int memo[2][1000];
int solve(bool f,int idx){
  if(idx==n){
    return 0;
  }
  if(memo[f][idx]!=-1){
    return memo[f][idx];
  }
  int ret=-1;
  if(f==false){
    ret=max(ret,max(solve(f,idx+1),solve(true,idx+1)+v[idx]));
  }else{
    ret=max(ret,solve(false,idx+1));
  }
  return memo[f][idx]=ret;
}
	    
int main(){
  cin>>n;
  for(int i=0;i<n;i++) cin>>v[i];
  memset(memo,-1,sizeof(memo));
  cout<<solve(false,0)<<endl;
  return 0;
}