#include <iostream>
#include <fstream>
#include <algorithm>
#include <cmath>

#include <string>
#include <vector>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <deque>
#include <queue>
#include <stack>

using namespace std;

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

typedef long long ll;

void Solve() {
    int n, k;
    ll sum;
    deque<ll> q;
    fin >> n >> k;
    vector<ll> v(n);
    for (int i = 0; i < n; ++i) {
        fin >> v[i];
    }

    for (int i = 0; i < k; ++i) {
        while (!q.empty() && q.back() > v[i]) {
            q.pop_back();
        }
        q.push_back(v[i]);
    }

    sum = q.front();
    for (int i = k; i < n; ++i) {
        if (q.front() == v[i - k]) {
            q.pop_front();
        }
        while (!q.empty() && q.back() > v[i]) {
            q.pop_back();
        }
        q.push_back(v[i]);
        sum += q.front();
    }
    fout << sum << '\n';
}

int main() {

    ios_base::sync_with_stdio(false);

    Solve();
    
    return 0;
}