#include <fstream>
using namespace std;

ifstream in("deq.in");
ofstream out("deq.out");

int v[5000001], deq[5000001];

int main()
{

    int n, k, left, right;
    long long sum;

    in >> n >> k;

    for (int i = 0; i < n; i++)
        in >> v[i];


    for (int i = 0; i < n; i++) {
        
        do
            if(left <= right && v[deq[right]] >= v[i])
                right--;
        while (left <= right && v[deq[right]] >= v[i]);
        

        right = right + 1;
        deq[right] = i;

        if (deq[left] <= i - k)
            left++;


        if (i >= k - 1) 
            sum += v[deq[left]];
    }

    out << sum;

    return 0;
}