#include<fstream>
#include<deque>
#define NMAX 5000010

using namespace std;

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

int n, k, i, a[NMAX];
long long sum;
deque<int> d;

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

    for (i=1; i<k; ++i)
    {
        f>>a[i];

        while (!d.empty() && a[d.back()]>a[i])
            d.pop_back();

        d.push_back(i);
    }

    for (i=k; i<=n; ++i)
    {
        f>>a[i];

        while (!d.empty() && a[d.back()]>a[i])
            d.pop_back();

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

        d.push_back(i);

        sum+=(long long)a[d.front()];
    }

    g<<sum<<"\n";
    f.close();
    g.close();
    return 0;
}