#include <bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

const int nmx = 5000010;
int a[nmx];
long long sum=0;
deque<int> d;
int main()
{

    int n, k;
    fin >> n >> k;
    for(int i=1; i<=n; i++)
        fin >> a[i];
    for(int i=1; i<=n; i++)
    {
        while(!d.empty() and a[i] <= a[d.back()]) d.pop_back();

        d.push_back(i);

        if(d.front() == i-k) d.pop_front();

        if(i >= k) sum += a[d.front()];
    }
    cout << sum;
}