#include <fstream>
#include <vector>
#include <deque>

std::ifstream f("deque.in");
std::ofstream g("deque.out");
std::deque<int> x;
std::vector<int> v;
int i, n, k, s, temp;

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