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

deque <int>D;
int a[5000005];
int n, k, x;
long long sum=0;

void cit_pana_k()
{
    scanf("%d", &a[1]);
    D.push_back(1);
    for(int i=2; i<=k; i++)
    {
        scanf("%d", &a[i]);
        while(!D.empty() && a[D.back()] >= a[i])
            D.pop_back();
        D.push_back(i);
    }
}


int main()
{
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
    scanf("%d %d", &n, &k);
    cit_pana_k();
    for(int i=k+1; i<=n; i++)
    {
        int vmpoz = D.front();
        while(vmpoz <= i-k-1)
        {
            D.pop_front();
            vmpoz = D.front();
        }
        sum += a[vmpoz];
        scanf("%d", &a[i]);
        while(!D.empty() && a[D.back()] >= a[i])
            D.pop_back();
        D.push_back(i);
    }
    int vmpoz = D.front();
    while(vmpoz <= n-k-1)
    {
        D.pop_front();
        vmpoz = D.front();
    }
    sum += a[vmpoz];
    printf("%lld", sum);
    return 0;
}