#include <bits/stdc++.h>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k,howmany,x;
deque<pair<int,int> >dq;
long long counter;
int main()
{
    fin>>n>>k;
    for(int i=1;i<=k;i++)
    {
        fin>>x;
        if(dq.empty())
        {
            dq.push_front({x,i});
            continue;
        }
        while(!dq.empty() && x<=dq.back().first)
            dq.pop_back();
        dq.push_back({x,i});
    }
    counter=dq.front().first;
    for(int i=k+1;i<=n;i++)
    {
        fin>>x;
        while(!dq.empty() && x<=dq.back().first)
            dq.pop_back();
        dq.push_back({x,i});
        if(dq.front().second==i-k)
            dq.pop_front();
        counter+=dq.front().first;
    }
    fout<<counter;
    return 0;
}