#include <iostream>
#include <fstream>

int deq[5000005];
int st = 0;
int dr = -1;

///deq [st] = deque.front()
///deq [dr] = deque.back();

void push_back(int x) {
    dr++;
    deq[dr] = x;
}

void pop_front() {
    // se elimina primul element
    st++;
}

void pop_back() {
    // se elimina ultimul element
    dr--;
};

int main() {

    std :: ifstream fin ("deque.in");
    std :: ofstream fout ("deque.out");
    int n, k, v[5000005];
    int suma =  0;
    fin >> n >> k;
    for (int i = 0; i < n; ++i) {
        fin >> v[i];
    }

    for (int i = 0; i < n; ++i) {
//        while (deque not empty and deque.back >= v[i])
        while(st <= dr and v[deq[dr]] > v[i]) {
            pop_back();
        }
        push_back(i);
//        if (deque.front == i-k)
        if (deq[st] == i-k) {
            pop_front();
            ///cand s-a atins limita de k elemnete
        }

        if (i >= k-1) {
//            std :: cout << v[deq[st]] << " " ;
            suma += v[deq[st]];
        }
    }
    fout << suma;
    return 0;
}