#include <fstream>
#include <deque>

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