#include <bits/stdc++.h>
#define MAXN 5000005

using namespace std;

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

deque <int> dq;
int v[MAXN], n, k;
long long s;

int main()
{
    in >> n >> k;
    for (int i=1; i<=n; i++)
        in >> v[i];
    for (int i=1; i<=n; i++)
    {
        while (!dq.empty() && v[i]<v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if (dq.front()==i-k)
            dq.pop_front();
        if (i>=k)
            s+=v[dq.front()];
    }
    out << s;
    return 0;
}