#include <fstream>
#define NMAX 5000000

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int n, k, A[NMAX], Deque[NMAX], st = 0, dr = -1;
long long sum;

int main()
{
    f>>n>>k;

    for(int i=1;i<=n;i++)
    {
        f>>A[i];

        while(st<=dr && A[i]<A[Deque[dr]])
            dr--;

        Deque[++dr]=i;

        if(Deque[st]==i-k)
            st++;

        if (i>=k)
            sum+=A[Deque[st]];
    }
    g<<sum;
    return 0;
}