#include <bits/stdc++.h>

using namespace std;

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

int a[5000002],n,k;
long long sum;
deque<int>q;
int main()
{
    fin>>n>>k;

    for(int i=1;i<=n;i++)
        fin>>a[i];
    for(int i=1;i<=n;i++)
    {
        while(!q.empty() && a[i]<=a[q.back()])
            q.pop_back();
        q.push_back(i);
        if(q.front()==i-k)q.pop_front();
        if(i>=k)sum+=a[q.front()];
       // fout<<sum<<" ";
    }
    fout<<sum;
    return 0;
}