#include <iostream>
#include<fstream>

using namespace std;

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

int deq[5000000], vec[5000000], head, rear, i, K, N, suma=0;

int main() {
    f >> N >> K;
    head = 1;
    rear = 0;

    for ( i=0; i < N; i++)
    {
        f >> vec[i];
        while(vec[i] <= vec[deq[rear]] && head <= rear)
            rear--;
        deq[++rear] = i;
        if(deq[head] == i - K)
            head++;
        if(i + 1 >= K)
            suma = suma + vec[deq[head]];
    }

    g << suma;

    return 0;
}