#include <fstream>
#include <vector>
#define NMAX 100005

using namespace std;

ifstream cin("oo.in") ;
ofstream cout("oo.out") ;

int N, v[NMAX], sol;
vector <int> Q;
vector <int> F;

int main()
{
 cin >> N ;
 for(int i = 1 ; i <= N ; ++ i)
 {
 	cin >> v[i] ;
 	Q.push_back(v[i]) ;
}

 int p =  Q.size() ;
 for(int i = 0 ; i < p / 2 ; i = i + 2)
    for(int j = p - 1 ; j > p / 2 ; j = j - 2)
 {
    if(Q[ i ] + Q[i + 1] > Q[ j ] + Q[ j - 1] )
    {
        sol = sol +(Q[i] + Q[i + 1]);
    }
    else {sol = sol + (Q[j] + Q[j - 1]); }
 }

cout << sol / 2 ;
	return 0;
}