#include <bits/stdc++.h>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque <int> dq;
long long n,k,totm,x[500001];
int main()
{
    fin >> n >> k;
    for (int i=1;i<=n;i++){
        fin >> x[i];
    }
    for (int i=1;i<=n;i++){
        while (!dq.empty() && x[i]<=x[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if (!dq.empty() && dq.front()==i-k)
            dq.pop_front();
        if (i>=k)
            totm+=x[dq.front()];
    }
    fout << totm;
    return 0;
}