#include <iostream>
#include <fstream>

using namespace std;
ifstream in ("deque.in");
ofstream out ("deque.out");

const int N=5000005;

int v[N],d[N],st,dr=-1,k,n;
long long s;

void stanga(int i)
{
    if(d[st]==i-k)
        st++;
}

void dreapta(int i)
{
    while(st<=dr && v[i]<= v[d[dr]])
        dr--;
    d[++dr]=i;
}

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