#include <iostream>
#include <fstream>
#include <deque>
using namespace std;

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

deque<int> q;
int n, k, i, a[5000005];
long long int s;

int main()
{
    f >> n >> k;
    for (i = 1; i <= k; i++)
    {
        f >> a[i];
        while (!q.empty() && q.back() > a[i])
            q.pop_back();
        q.push_back(a[i]);
    }
    s += q.front();

    for (i = k + 1; i <= n; i++)
    {
        f >> a[i];
        while (!q.empty() && q.back() > a[i])
            q.pop_back();
        q.push_back(a[i]);
        if (q.front() == a[i - k])
            q.pop_front();
        s += q.front();
    }

    g << s;
}