#include <bits/stdc++.h>

using namespace std;

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

const int nmax=5e6+5;

deque <int> dq;
int n, k, v[nmax];

void read ()
{
    fin >> n >> k;
    for (int i=1; i<=n; i++)
        fin >> v[i];
}

void solve ()
{
    long long sum=0;
    for (int i=1; i<=n; i++)
    {
        while (!dq.empty() && v[i]<=v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if (i>=k)
        {
            while (!dq.empty() && i-dq.front()>=k)
                dq.pop_front();
            sum+=v[dq.front()];
        }
    }
    fout << sum;
}

signed main()
{
    read();
    solve();
    return 0;
}