#include <fstream>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");

#define nmax 5000010

int n,k,v[nmax],dq[nmax],st,dr;
long long s;

int main()
{
    int i,j;
    cin>>n>>k;
    st=1;
    for (i=1;i<=n;i++)
    {
        cin>>v[i];
        while (st<=dr && v[i]<=v[dq[dr]])
            dr--;
        dq[++dr]=i;
        if (dq[st]==i-k)
            st++;
        if(i>=k)
            s+=v[dq[st]];
    }
    cout<<s;
}