#include <bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
const int Nmax = 5000500;
long long sum = 0;
int n,k,i;
int a[Nmax];
deque <int> coada;

int main (){
    fin>>n>>k;
    for (i=1;i<=n;i++)
        fin>>a[i];
    for (i=1;i<=k;i++){
        while (!coada.empty()){
            if (a[i]>=coada.back())
                break;
            coada.pop_back();
        }
        coada.push_back(a[i]);
    }
    sum+=coada.front();
    for (i=k+1;i<=n;i++){
        while (!coada.empty()){
            if (a[i]>=coada.back())
                break;
            coada.pop_back();
        }
        coada.push_back(a[i]);
        if (coada.front()==a[i-k])
            coada.pop_front();
        sum+=coada.front();
    }
    fout<<sum;
}