#include<bits/stdc++.h>
#define mp make_pair
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque<pair<int, int> >dq;
long long int v,k,n,suma=0;
int main(){

    fin>>n>>k;
    for (int i=1;i<=k;i++)
    {
        fin>>v;
        pair<int, int>x = mp(v,i);
        while (!dq.empty() && dq.back().first>v)
        {
            dq.pop_back();
        }
        dq.push_back(x);
    }
    suma+=dq.front().first;
    for (int i=k+1;i<=n;i++)
    {
        fin>>v;
        while (dq.front().second<=i-k)
        {
            dq.pop_front();
        }
        pair<int,int>x=mp(v,i);
        while (!dq.empty() && dq.back().first>v)
        {
            dq.pop_back();
        }
        dq.push_back(x);
        suma+=dq.front().first;

    }
    fout<<suma;
}