#include <fstream>
#include <deque>

using namespace std;

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

deque <int> D;
int n, k, i, v[5000000];
long long int s;

int main()
{
    f>>n>>k;
    for (i=1;i<=n;i++)
        f>>v[i];

    for (i=1;i<=n;i++)
    {
        while (!D.empty() && v[D.back()]>=v[i])
            D.pop_back();
        D.push_back(i);
        if (i-k==D.front())
            D.pop_front();
        if (i-k+1>0) s+=v[D.front()];
    }
    g<<s;
    return 0;
}