#include <bits/stdc++.h>

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

int main() {
    int n, k;
    fin>>n>>k;

    vector<int> a(n+1);
    for (int i=1; i<=n; ++i) fin>>a[i];

    deque<int> q;
    for (int i=1; i<=k; ++i) {
        while (!q.empty() && a[q.back()] >= a[i]) q.pop_back();
        q.push_back(i);
    }

    long long S = a[q.front()];
    for (int i=k+1; i<=n; ++i) {
        while (!q.empty() && q.front() <= i-k) q.pop_front();
        while (!q.empty() && a[q.back()] >= a[i]) q.pop_back();
        q.push_back(i);
        S += a[q.front()];
    }

    fout<<S;
}