#include <fstream>

using namespace std;

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

long long NR[5000500];

class Deque{
    struct node{
        int nr;
        node *prev = NULL;
        node *next = NULL;
    };
    int size = 0;
    node *pos_front = NULL;
    node *pos_back = NULL;
public:
    bool empty(){
        if (size == 0){
            return 1;
        }
        return 0;
    };
    void push_front(int val){
        size ++;
        node *now = new node();
        now -> nr = val;
        if (pos_front != NULL){
            now -> prev = pos_front;
            pos_front -> next = now;
        }
        pos_front = now;
        if (pos_back == NULL){
            pos_back = now;
        }
    };
    void push_back(int val){
        size ++;
        node *now = new node();
        now -> nr = val;
        if (pos_back != NULL){
            now -> next = pos_back;
            pos_back -> prev = now;
        }
        pos_front = now;
        if (pos_front == NULL){
            pos_front = now;
        }
    };
    void pop_front(){
        if (pos_front == NULL){
            return;
        }
        size --;
        if (pos_front -> prev != NULL){
            pos_front = pos_front -> prev;
            delete pos_front -> next;
            pos_front -> next = NULL;
        }
        else{
            delete pos_front;
            pos_front = NULL;
            pos_back = NULL;
        }
    };
    void pop_back(){
        if (pos_back == NULL){
            return;
        }
        size --;
        if (pos_back -> next != NULL){
            pos_back = pos_back -> next;
            delete pos_back -> prev;
            pos_back -> prev = NULL;
        }
        else{
            delete pos_back;
            pos_front = NULL;
            pos_back = NULL;
        }
    };
    int front(){
        return pos_front -> nr;
    };
    int back(){
        return 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];
    }
    int full = n - k + 1;
    for (int i=1; i<=k; i++){
        if (!D.empty() && NR[i] > NR[D.front()] && i > full){
            continue;
        }
        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();
        }
        if (!D.empty() && D.back() <= i - k){
            D.pop_back();
        }
        D.push_front(i);
        cont += NR[D.back()];
    }
    cout<<cont;
    return 0;
}