#include <bits/stdc++.h>

using namespace std;
ifstream fin ("deque.in");
ofstream fout ("deque.out");
int v[5000001];
deque<int>q;
int main()
{
    int n,k;
    long long s=0;
    fin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        fin>>v[i];
        while(!q.empty() && v[i]<=v[q.back()])
            q.pop_back();
        q.push_back(i);
        if(i>=k)
        {
            if(q.front()==i-k)
                q.pop_front();
            s+=v[q.front()];
        }
    }
    fout<<s;
    return 0;
}