#include <iostream>
#include <fstream>
using namespace std;
int d[5000001],v[5000001],st=1 ,dr,n,k;
void stanga(int i)
{
    if(i-d[st]==k)
        st++;
}
void dreapta (int i)
{
    while(st<=dr && v[i]<=v[d[dr]])
        dr--;
    d[++dr]=i;

}
int main()
{
    int i;
    long long s;
    ifstream in("deque.in");
    ofstream out("deque.out");
    in>>n>>k;
    s=0;
    for(i=1; i<=n; i++)
        in>>v[i];
    for(i=1; i<=n; i++)
    {
        if(i>k)
            stanga(i);
        dreapta(i);
        if (i >= k) s+=v[d[st]];
    }
    out<<s;
    return 0;
}