#include <fstream>
#include <deque>

using namespace std;
ifstream a ("deque.in");
ofstream b ("deque.out");

deque <int> q;
int n,i,k,v[5000010];
long long Suma;
int main()
{
    a>>n>>k;
    for (i=1;i<=n;i++)
    {
        a>>v[i];
        while (!q.empty()&&v[q.front()]>v[i])q.pop_front();
        q.push_front(i);
        if (i>=k)
        {
            if (q.back()<i-k+1)q.pop_back();
            Suma+=v[q.back()];
        }
    }
    b<<Suma;
    return 0;
}