#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

int n, k, v[5000000];
long long s;
deque<int>d;

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