#include <fstream>

using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
long long s,mn=99999999,i,d,a[5000005],n,k;
int main()
{
    cin>>n>>k;
    for(i=1;i<=n;i++)
    {
        cin>>a[i];
        if(i<=k&&a[i]<mn)
        {
            mn=a[i];
        }
    }
    s=mn;
    //cout<<mn<<" ";
    for(i=k+1;i<=n;i++)
    {
        if(a[i]<mn)
        {
            mn=a[i];
        }
        if(mn==a[i-k])
        {
            mn=9999999999999;
            for(d=i-k+1;d<=i;d++)
            {
                if(a[d]<mn)
                {
                    mn=a[d];
                }
            }
        }
        s=s+mn;
        //cout<<mn<<" ";
    }
    cout<<s;
    return 0;
}