#include <iostream>
#include <fstream>

using namespace std;

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


int main()
{
    int n, k, l, r;
    long long int sum;
    f >> n >> k;
    int v[n], deq[n];
    for (int i = 0; i < n; i++)
        f >> v[i];
    l = 0;
    r = -1;
    sum = 0;
    for (int i = 0; i < n; i++){
        while(l <= r && v[i] < deq[r])
            r--;
        r++;
        deq[r] = v[i];
        if(i - k >= 0 && deq[l] == v[i - k]){
            l++;
        }
        if(i >= k-1)
            sum += deq[l];
    }
    g << sum;

    return 0;
}