3x2.cpp

// NOTE: it is recommended to use this even if you don't understand the following code.

#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>

using namespace std;

long long N;
vector<long long> P;

int main() {
//  uncomment the following lines if you want to read/write from files
	//ifstream cin("input.txt");
	//ofstream cout("output.txt");

    cin >> N;
    P.resize(N);
    for(long long i = 0; i < N; i++)
        cin >> P[i];

    // insert your code here
    long long ans=0;
    
    sort(P.begin(), P.end());
    reverse(P.begin(), P.end());
    
    for (long long i=0; i<N; i++) {
    	if ((i+1)%3 != 0) {
    		ans += P[i];
		}
	}
	    
    cout << ans << endl; // print the result
    return 0;
}