#include <bits/stdc++.h>

using namespace std;

int a[5000001], ind[5000001];

int main()
{
    int n, k;
    int64_t suma=0;
    ifstream f("deque.in");
    ofstream g("deque.out");

    f>>n>>k;
    for(int i=1;i<=n;++i)
    {
        f>>a[i];
    }

    int s=1, d=0;
    for(int i=1; i<=n; ++i)
    {
        while(s<=d && a[i]<=a[ind[d]])
        {
            d--;
        }
        d++;
        ind[d]=i;
        if(ind[s]==i-k)
        {
            s++;
        }
        if(i>=k)
        {
            suma+=a[ind[s]];
        }


    }
    g<<suma;
    return 0;
}