#include<cstdio>
#include<algorithm>
#define MAX_N 1000010
using namespace std;

int n,t;
long long a[MAX_N];
long long qs[MAX_N];
long long ans;

int main()
{
    scanf("%d%d",&n,&t);
    for(int c=1;c<=n;c++) scanf("%lld",&a[c]);
    for(int c=1;c<=n;c++) qs[c] = qs[c-1] + a[c];

    if( n == 1 )
    {
        printf("%lld\n",a[1]*(t/2+1));
        return 0;
    }

    for(int c=2;c<=n and c<=t+1;c++)
    {
        long long tmp = qs[c];
        int rem = t+1-c;
        tmp += ((rem+1)/2)*a[c-1];
        tmp += (rem/2)*a[c];
        ans = max( ans , tmp );
    }
    printf("%lld\n",ans);
}