#include <bits/stdc++.h>

using namespace std;
ifstream fin ("deque.in");
ofstream fout ("deque.out");
deque <int> q;
int i,n,k,s,a[5000005];
int main()
{
    fin>>n>>k;
    for (i=1; i<=k; i++)
    {
        fin>>a[i];
        while (!q.empty () && a[i]<=a[q.back()]) q.pop_back();
        q.push_back(i);
    }
    s=a[q.front()];
    for (i=k+1; i<=n; i++)
    {
        fin>>a[i];
        while (!q.empty() && i-q.front()>=k) q.pop_front();
        while (!q.empty() && a[i]<a[q.back()]) q.pop_back ();
        q.push_back(i);
        s+=a[q.front()];
    }
    fout<<s;
    return 0;
}