#include <fstream>

using namespace std;

unsigned int N, K;
int a[5000001];

int Deque[5000001];
int Front, Back;
unsigned int i;

long long int sum;

int main ()
{
    ifstream fin ("deque.in");
    fin >> N >> K;
    for (i=1; i<=N; i++)
        fin >> a[i];
    fin.close();
    Front = 1;
    for (i=1; i<=N; i++)
    {
        while (Front <= Back && a[i] <= a[Deque[Back]])
            Back--;
        Deque[++Back] = i;
        if (Deque[Front] == i-K)
            Front++;
        if (i >= K)
            sum += a[Deque[Front]];
    }
    ofstream fout ("deque.out");
    fout << sum;
    fout.close();
    return 0;
}