#include <fstream>
#include <deque>

using namespace std;

deque <int>dq;
const int N = 5000000;

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

int v[N+1];

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