#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k,v[5000001];
long long s;
deque<int> dq;
int main() {
    fin>>n>>k;
    for (int i=1;i<=n;i++)
        fin>>v[i];
    dq.push_back(1);
    for (int i=2;i<=n;i++) {
        while (!dq.empty() && v[i]<=v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if (i-dq.front()+1>k)
            dq.pop_front();
        if (i>=k)
            s+=v[dq.front()];
    }
    fout<<s;
    return 0;
}