#include <fstream>
#include <deque>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

deque<int> d;
int n, k, v[5000005];
long long s;

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