#include <fstream>

using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");

int a[5000001];
int deq[5000001];

int main()
{
    int n;
    int k;
    long long sum = 0;
    int s = 0 ,d = -1;

    in >> n >> k;
    for(int i=0; i<n; i++)
        in >> a[i];
    for(int i=0; i<n; i++)
        {
            while(s <= d && a[i] <= a[deq[d]])
                d--;
            deq[++d] = i;
            if(deq[s] == i-k)
                s++;
            if(i+1 >= k)
                sum = sum + a[deq[s]];
        }
    out << sum;
    in.close();
    out.close();
    return 0;
}