#include <bits/stdc++.h>

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");
long long n, k, i, a[5000002], s;
deque<long long> q;

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

    return 0;
}