#include<iostream>
#include<fstream>
#include<vector>
#include<unordered_map>
#include<algorithm>
#include<queue>
#include<stack>
#include<deque>
using namespace std;

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

/*struct Node {
    int data;
    Node* left;
    Node* right;
    Node(int val) : data(val), left(nullptr), right(nullptr) {}
};

class InorderIterator {
    stack<Node*> st;

    void move_left(Node* node) {
        while (node != nullptr) {
            st.push(node);
            node = node->left;
        }
    }
public:
    InorderIterator(Node* root) {
        move_left(root);
    }

    bool hasNext() {
        return !(st.empty());
    }

    Node* next() {
        if (st.empty()) {
            throw "NO NEXT";
        }
        Node* current_node = st.top();
        st.pop();
        if (current_node->right != nullptr) {
            move_left(current_node->right);
        }

        return current_node;
    }
};*/

int n;
int number;

deque<pair<int, int>> dq;

///1 2 3 4 5 6 7 8
int main() {
    ios_base::sync_with_stdio(false);
    fin.tie(NULL);

    int k;
    long long answer_sum;

    fin >> n >> k;
    answer_sum = 0;
    for (int i = 1; i <= n; i++) {
        fin >> number;

        //elimin elementele mai mari de la finalul deque ului
        while (!dq.empty() && dq.back().first >= number) {
            dq.pop_back();
        }
        dq.push_back({ number, i });
        if (!dq.empty() && dq.front().second <= i - k) {
            dq.pop_front();
        }
        if (i >= k) {
            //cout << "***" << dq.front().first << "\n";
            answer_sum += dq.front().first;
        }
    }

    fout << answer_sum << "\n";

    fin.close();
    fout.close();
    return 0;
}