#include <iostream>
#include<vector>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n;
    cin>>n;
    vector<long long>a(2*n+5);
    vector<long long>prefix(2*n+5);
    vector<int>id(2*n+5);
    vector<long long>res(2*n+5);
    for(int i=1;i<=2*n;i++){
        cin>>a[i];
        prefix[i]=prefix[i-1]+a[i];
        if(id[a[i]]){
            res[i]=res[id[a[i]]-1]+prefix[i]-prefix[id[a[i]]-1];
        }
        else id[a[i]]=i;
        res[i]=max(res[i],res[i-1]);
    }
    cout<<res[2*n]<<endl;
    return 0;
}
// 64 位输出请用 printf("%lld")