#include <iostream>
#include <vector>

int main()
{
	int nArray;
	std::cin >> nArray;
	
	std::vector<long long> arr(nArray);
	for (int i = 0; i < nArray; ++i) std::cin >> arr[i];
	
	long long maxFound = 0;
	for (int i = 0; i < nArray-1; ++i)
	{
		long long sum = arr[i];
		long long squaresum = arr[i]*arr[i];
		for (int j = i+1; j < nArray; ++j)
		{
			sum += arr[j];
			squaresum += arr[j] * arr[j];
			
			maxFound = std::max(maxFound, (sum * sum - squaresum) / 2);
		}
	}
	
	std::cout << maxFound << '\n';
	
	return 0;
}