#include <fstream>
#include <vector>
#include <algorithm>
#include <deque>

using namespace std;

ifstream cin ("deque.in" );
ofstream cout("deque.out");

long long n, k, s = 0, x, q;
deque <int> d;

int main()
{
    cin >> n >> k;

    for (int i = 0; i < k - 1; i++)
    {
        cin >> x;
        d.push_back(x);
    }
    q = *(min_element(d.begin(), d.end()));

    for (int i = k - 1; i < n; i ++)
    {
        cin >> x;
        d.push_back(x);
        if (x < q) q = x;
        s += q;
        x = d[0];
        d.pop_front();
        if (x == q) q = *(min_element(d.begin(), d.end()));
    }

    cout << s;

    return 0;
}