#include <iostream>
#include <bits/stdc++.h>
using namespace std;
int main()
{
long long int n, t;
cin >> n >> t;
long long int arr[n];
for (long long int i = 0; i < n; ++i)
{
/* code */cin >> arr[i];
}
long long int ans = 0;
long long int sum = 0;
long long int maxm = -1;
if(n == 1)
{
cout << ((t/2) + 1) * arr[0] << endl;
return 0;
}
for (long long int i = 0; i < n - 1; ++i)
{
long long int HD = i;
if(HD > t) break;
sum += arr[i];
long long int SY = sum;
long long int RT = t - HD;
SY += (RT/2) * (arr[i] + arr[i + 1]);
if(RT&1) SY += arr[i + 1];
maxm = max(maxm, SY);
}
cout << maxm ;
return 0;
}
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