#include <iostream>
#include <fstream>
using namespace std;
ifstream in ("deque.in");
ofstream out ("deque.out");
int n,v[5000001],deq[5000001];
int main()
{
    long long n,k,i,s=1,d=0;
    long long suma=0;
    in>>n >>k;
    for (i=1;i<=n;++i)
    {
        in >> v[i];
        if (s<=d && deq[s]==i-k)
            {
                s++;
            }
        while (s<=d && v[i]<=v[deq[d]])
        {
            d--;
        }
        deq[++d]=i;
        if (i>= k)
        suma+=v[deq[s]];
         //cout << v[deq[s]] << ' ';}
    }
    out << suma;
    return 0;
}
//ttps://infoarena.ro/problema/branzalllllllllaafsafsafa