#include <bits/stdc++.h>

using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque<int> deq;
int i,j,k,v[100000001],n,m;
long long sum;
int main()
{
    f>>n>>k;
    for(i=1; i<=n; i++)
        f>>v[i];
    for(i=1;i<=n;i++)
    {
        while(deq.empty() == false and v[i] <= v[deq.back()])
        {
            deq.pop_back();
        }
        deq.push_back(i);
        if(i>=k)
        {
            sum = sum+v[deq.front()];
            if(deq.front()<=(i-k+1))
                deq.pop_front();
        }

    }
    g<<sum;
    return 0;
}