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

//#define SHOWARRY(a) {printf("---"#a"---\n");for(int i=0;i<n;++i){printf("%4d\n",a[i]);}printf("----\n");}

int main() {
	std::ios::sync_with_stdio(false);
	std::cin.tie(0);

	int n;
	std::cin >> n;
	std::vector<int> v(n, 0);
	std::vector<int> check(n, 0);
	for (int i = 0; i < n; ++i) {
		std::cin >> v[i];
	}
	int sum = 0;
	switch (n) {
	case 1:
		sum = v[0];
		break;
	case 2:
		sum = (v[0] < v[1]) ? v[1] : v[0];
		break;
	case 3:
		sum = (v[0] + v[2] < v[1]) ? v[1] : v[0] + v[2];
		break;
	default:
		for (int i = 0; i < n - 3; ++i) {
			int tmp1 = v[i] + v[i + 2];
			int tmp2 = v[i] + v[i + 3];
			int tmp3 = v[i + 1] + v[i + 3];
			int tmp = std::max({ tmp1, tmp2, tmp3 });
			if (tmp == tmp1) {
				++check[i];
				++check[i + 2];
			}
			else if (tmp == tmp2) {
				++check[i];
				++check[i + 3];
			}
			else if (tmp == tmp3) {
				++check[i + 1];
				++check[i + 3];
			}
		}//SHOWARRY(check);
		for (int i = 0; i < n - 1; ++i) {
			if (check[i] > 0 && check[i + 1] > 0) {
				if (v[i] < v[i + 1]) {
					check[i] = 0;
				}
				else {
					check[i + 1] = 0;
				}
			}
		}//SHOWARRY(check);
		for (int i = 0; i < n; ++i) {
			if (check[i] > 0) {
				sum += v[i];
			}
		}
		break;
	}
	
	std::cout << sum << "\n";

	return 0;
}