#include <fstream>
#include <iostream>

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

int N, K;
long long sum = 0;

int main()
{
    fin >> N >> K;
    int deque[N], poz[N];

    int back = -1, front = 0;
    for(int i = 0; i < N; i++)
    {
        fin >> deque[i];
        while(front <= back and deque[i] <= deque[back])
            back--;

        deque[++back] = deque[i];
        poz[back] = i;

        if(poz[front] == i - K)
            front++;

        if(i + 1 >= K)
            sum += deque[front];
    }


    fout << sum;
    return 0;
}