#include <fstream>
#include <deque>
#include <vector>
using namespace std;

int n, k;
const int Inf = 10000001;
deque<int> dq;
vector<int> a(5000001);

int main() {
    int i, Min_cur = Inf, x;
    long long suma = 0;

    ifstream f("deque.in");
    f >> n >> k;
    
    for (i = 1; i <= n; i++)
        f >> a[i];
    f.close();

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

    ofstream g("deque.out");
    g << suma;
    g.close();

    return 0;
}