#include <fstream>
#include <deque>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
deque<int> dq;
static int v[5000002];
int main() {
    int st,dr,n,k;
    long long s=0;
    in>>n>>k;
    for(int i=0;i<n;i++)
        in>>v[i];
    st=0;
    dr=1;
    for(int i=0;i<n;i++)
    {
        if(!dq.empty() && dq.front()==i-k)
        {
            dq.pop_front();
        }
        while(!dq.empty() && v[i]<=v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(i>=k-1)
        {
            s+=v[dq.front()];
        }
    }
    out<<s;
    return 0;
}