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

ifstream in("deque.in");
ofstream out("deque.out");
const int N=5000001;
int st, dr = -1, d[N], v[N],k,n;

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,S=0;
    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=S+v[d[st]];
    }
    out<<S;
    return 0;
}