#include <bits/stdc++.h>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque<pair<int,int>>dq;
int main()
{
    int n,k,x;
    fin>>n>>k;
    fin>>x;
    dq.push_back({x,1});
    for(int i=2; i<=k; i++)
    {
        fin>>x;
        while(!dq.empty() && x<=dq.back().first)
            dq.pop_back();
        dq.push_back({x,i});
    }
    long long sum=dq.front().first;
    //cout<<dq.front().first<<" "<<dq.back().first<<endl;
    for(int i=k+1;i<=n;i++)
    {
        fin>>x;
        while(!dq.empty() && i-dq.front().second>=k)
            dq.pop_front();
        while(!dq.empty() && x<=dq.back().first)
            dq.pop_back();
        dq.push_back({x,i});
        sum+=dq.front().first;
        //cout<<dq.front().first<<" "<<dq.back().first<<endl;
    }
    fout<<sum;
    return 0;
}