#include <bits/stdc++.h>
#define N 5000200
using namespace std;

ifstream fin ("deque.in");
ofstream fout ("deque.out");

deque <int> dq;
long long a[N], n, k;

int main()
{
    fin>>n>>k;
    for (int i=1; i<=n; ++i)
        fin>>a[i];
    fin.close();

    long long sum=0;

    for (int i=1; i<=n; ++i)
    {
        while (!dq.empty() && a[i]<=a[dq.back()]) dq.pop_back();
        dq.push_back(i);
        if (dq.front()==i-k) dq.pop_front();

        if (i>=k) sum+=a[dq.front()];
    }
    fout<<sum<<'\n';
    fout.close();
    return 0;
}