#include <fstream>
#include <deque>

using namespace std;

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

int v[5000005];
deque<int> dg;

long long deq(int n, int k)
{
    long long s = 0;
    for(int i = 0; i<n; i++)
    {
        in >> v[i];
        if(!dg.empty() && dg.front() == i-k)
            dg.pop_front();

        while(!dg.empty() && v[i] <= v[dg.back()])
            dg.pop_back();

        dg.push_back(i);
        if(i >= k-1)
            s += v[dg.front()];

    }
    return s;
}
int main()
{
    int n, k;
    in >> n >> k;
    out << deq(n,k);
    return 0;
}