#include <fstream>
#define maxn 5000010
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,i,k;
int a[maxn], d[maxn];
int front, back;
long long Sum;
int main()
{
    fin>>n>>k;
    for(i=1;i<=n;i++)
    fin>>a[i];
    front=1;back=0;
    for (i = 1; i <= n; i++)
    {
        while (front <= back && a[i] <= a[d[back]])
            back--;
        d[++back] = i;
        if (d[front] == i-k)
            front++;
        if (i >= k) Sum += a[ d[front]];
    }
    fout<<Sum;
    return 0;
}