#include <bits/stdc++.h>

using namespace std;

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

deque<pair<int,int> > deq;
int n,k,a,sum,i;

int main()
{
    fin>>n>>k;
    for(i=0; i<k; i++)
    {
        fin>>a;
        while(!deq.empty() && deq.back().first>=a) deq.pop_back();
        deq.push_back(make_pair(a,i));
    }
    sum+=deq.front().first;
    for(i=k; i<n; i++)
    {
        fin>>a;
        while(!deq.empty() && deq.back().first>a) deq.pop_back();
        deq.push_back(make_pair(a,i));
        if(deq.front().second<=i-k)
        {
            deq.pop_front();
        }
        sum+=deq.front().first;
    }
    fout<<sum;
    return 0;
}