#include <cstdio>
#include <algorithm>

long long n, t, polany[1000005], poprzednia, j, l, suma, maxsuma, z, sumy[1000005];

int main()
{
	scanf("%lld%lld", &n, &t);
	for (int i = 0; i < n; i++)
	{
		scanf("%lld", &polany[i]);
	}
	sumy[0] = polany[0];
	for (int i = 1; i < n; i++)
	{
		sumy[i] = sumy[i - 1] + polany[i];
	}
	for (int i = 0; i < n - 1; i++)
	{
		if ((t - i) % 2 == 0)
			suma = (t - i) / 2 * polany[i] + (t - i) / 2 * polany[i + 1];
		else
			suma = (t - i) / 2 * polany[i] + (t - i) / 2 * polany[i + 1] + polany[i + 1];
		suma += sumy[i];
		maxsuma = std::max(suma, maxsuma);
		suma = 0;
	}
	printf("%lld", maxsuma);
	getchar();
	getchar();
	return 0;
}