#include <iostream>
#include <fstream>
using namespace std;

int d[5000001], v[5000001];

int main()
{
    int i, n, k, st, dr;
    long long s;
    ifstream f ("deque.in");
    ofstream g ("deque.out");
    f>>n>>k;
    for (i=0; i<n; i++) f>>v[i];
    st=0;
    dr=-1;
    s=0;
    for (i=0; i<n; i++)
    {
        //elimin din stanga
        if (st<=dr && d[st]==i-k)
        {
            st++;
        }
        //elimin din dreapta
        while (st<=dr && v[i]<=v[d[dr]])
        {
            dr--;
        }
        //adaug elementul curent
        d[++dr]=i;
        if (i>=k-1)
        {
            s+=v[d[st]];
        }
    }
    g<<s;
}