#include <fstream>
#include <vector>

using namespace std;

ifstream cin("deque.in");
ofstream cout("deque.out");

long long NR[5000500];

struct node{
    int nr;
    int pos;
    int prev = -1;
    int next = -1;
};

vector <node> N;

class Deque{
    int pos_front = -1;
    int pos_back = -1;
public:
    bool empty(){
        if (pos_front == -1){
            return 1;
        }
        return 0;
    };
    void push_front(int val){
        node now;
        N.push_back(now);
        N[N.size() - 1].nr = val;
        N[N.size() - 1].pos = N.size() - 1;
        if (pos_front != -1){
            N[N.size() - 1].prev = pos_front;
            N[pos_front].next = N.size() - 1;
        }
        pos_front = N.size() - 1;
        if (pos_back == -1){
            pos_back = N.size() - 1;
        }
    };
    void push_back(int val){
        node now;
        N.push_back(now);
        N[N.size() - 1].nr = val;
        N[N.size() - 1].pos = N.size() - 1;
        if (pos_back != -1){
            N[N.size() - 1].next = pos_back;
            N[pos_back].prev = N.size() - 1;
        }
        pos_back = N.size() - 1;
        if (pos_front == -1){
            pos_front = N.size() - 1;
        }
    };
    void pop_front(){
        if (pos_front == -1){
            return;
        }
        if (N[pos_front].prev != -1){
            N[N[pos_front].prev].next = -1;
            //cout<<N[N[pos_front].prev].pos<<'\n';
            pos_front = N[N[pos_front].prev].pos;
            N[pos_front].prev = -1;
        }
        else{
            pos_front = -1;
            pos_back = -1;
        }
    };
    void pop_back(){
        if (pos_back == -1){
            return;
        }
        if (N[pos_back].next != -1){
            N[N[pos_back].next].prev = -1;
            pos_back = N[N[pos_back].next].pos;
            N[pos_back].next = -1;
        }
        else{
            pos_back = -1;
            pos_front = -1;
        }
    };
    int front(){
        if (pos_front == -1){
            return -1e9;
        }
        return N[pos_front].nr;
    };
    int back(){
        if (pos_back == -1){
            return -1e9;
        }
        return N[pos_back].nr;
    };
} D;

int main() {

    ios::sync_with_stdio(false);
    cin.tie(NULL);

    long long cont = 0;
    int n, k;
    cin>>n>>k;
    for (int i=1; i<=n; i++){
        cin>>NR[i];
    }
    for (int i=1; i<=k; i++){
            while(!D.empty() && NR[D.front()] > NR[i]){
                D.pop_front();
            }
        D.push_front(i);
    }
    cont += NR[D.back()];
    for (int i=k+1; i<=n; i++){
            while(!D.empty() && NR[D.front()] > NR[i]){
                D.pop_front();
            }
        D.push_front(i);
        if (D.back() <= i - k){
            D.pop_back();
        }
        cont += NR[D.back()];
    }
    cout<<cont;
    return 0;
}