#include <bits/stdc++.h>

using namespace std;
int v[5000010];
int main() {
    ifstream cin("deque.in");
    ofstream cout("deque.out");
    int n, k, i;
    long long s=0;
    cin >> n >> k;
    deque < int > Q;
    for (int i = 1; i <= n; i++) {
        cin >> v[i];

    }
    for(int i = 1; i <= n; i++) {
        while (Q.empty() == false && v[i] <= v[Q.back()]) {
            Q.pop_back();
        }
        Q.push_back(i);
        if(i >= k) {
            s += v[Q.front()];
            if(Q.front() == i - k + 1) {
                Q.pop_front();
            }
        }
    }
    cout << s;
    return 0;
}