#include <iostream>
#include <fstream>
#include <set>

using namespace std;

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

int a[5000000];
multiset <int> S;

int main()
{
    int n, k;
    f >> n >> k;
    for (int i = 0; i < n; i++)
    {
        f >> a[i];
    }
    for (int i = 0; i < k; i++)
    {
        S.insert(a[i]);
    }
    long long s = *S.begin();
    for (int i = k; i < n; i++)
    {
        S.erase(a[i - k]);
        S.insert(a[i]);
        s += *S.begin();
    }
    g << s;
}