#include <bits/stdc++.h>

using namespace std;

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

struct nr{
    int val;
    int poz;
};

deque<nr> v;
int S = 0;

int main()
{
    int n,k,i;
    nr aux;
    fin>>n>>k;
    for(i = 1; i <= n; i++){
        fin>>aux.val;
        aux.poz = i;
        v.push_back(aux);
        while(v.front().poz <= i-k || v.front().val > aux.val){
            v.pop_front();
        }
        if(i-k >= 0)
            S += v.front().val;
    }
    fout<<S<<endl;
    return 0;
}